1 letter:
r

2 letters:
ar, r.

3 letters:
are, bar, car, dar, far, gar, har, jar, lar, mar, npr, par, sar, tar

4 letters:
adar, afar, ajar, alar, barr, carr, char, czar, fahr, haar, parr, saar, scar, spar, star, thar, tsar, voir

5 letters:
akbar, asarh, athar, aurar, babar, barre, bazar, bihar, boyar, charr, cigar, dakar, damar, debar, dinar, gidar, iyyar, kotar, lamar, lidar, lobar, maher, malar, mylar, qatar, radar, rebar, safar, selar, sitar, sizar, starr, t-bar, talar, velar, vidar

6 letters:
alegar, anshar, avatar, bazaar, bonior, boxcar, bulbar, busbar, by far, calcar, caspar, caviar, cottar, deodar, devoir, disbar, gaidar, go far, guitar, instar, isobar, jaguar, jamjar, kishar, lontar, lumbar, magyar, memoir, nascar, nuphar, sambar, secpar, sirdar, so far, trocar, veadar

7 letters:
alcazar, astylar, bizarre, caviare, co-star, crowbar, daystar, escobar, flatcar, handcar, hectare, jacamar, malabar, minibar, minicar, myanmar, navarre, not far, nut bar, pissoir, pry bar, railcar, samovar, sandbar, seminar, shophar, sidebar, sidecar, taskbar, tollbar, toolbar, tramcar, tv star, vitharr, wet bar, who are, you are

8 letters:
a. t. r., abattoir, all-star, axle bar, baccilar, bell jar, bog star, c. p. r., caryocar, cash bar, cinnabar, coal car, coal tar, condylar, crossbar, date bar, dog star, f. d. r., feldspar, gill bar, grab bar, grimoire, high bar, horsecar, issachar, loadstar, lodestar, mail car, microbar, milk bar, millibar, motorcar, nenuphar, nightjar, p. c. r., pace car, peignoir, pine tar, polestar, r. j. r., race car, sand bar, scimitar, sea star, slop jar, stockcar, tank car, thus far, unifilar, v. c. r., voussoir, what are, wood tar, zanzibar

9 letters:
abreuvoir, au revoir, blue star, cabin car, cable car, candy bar, carob bar, chair car, colcothar, color bar, commissar, earthstar, film star, fluorspar, fruit bar, handlebar, hekmatyar, in so far, kala-azar, mason jar, metal bar, pinch bar, pourboire, prowl car, registrar, reservoir, rock star, salad bar, scout car, slice bar, snack bar, space bar, sport car, squad car, stall bar, stock car, streetcar, superstar, sushi bar, there are, towel bar, where are

10 letters:
almacantar, belshazzar, buffet car, bumper car, cattle car, coffee bar, cookie jar, dining car, double bar, escritoire, estate car, fixed star, flare star, giant star, heavy spar, jaunty car, leyden jar, movie star, north star, opera star, oyster bar, palace car, parlor car, patrol car, peanut bar, polar star, police car, racing car, repertoire, sports car, texas star, track star

11 letters:
amphistylar, apricot bar, arctic char, baggage car, basket star, binary star, brittlestar, bronze star, compact car, double star, dyaus-pitar, freight car, golden star, gondola car, granola bar, hershey bar, iraqi dinar, liquidambar, mineral tar, naval radar, parlour car, pullman car, railway car, ripping bar, silver star, smoking car, touring car, trolley car, ulaanbaatar

12 letters:
aide-memoire, blazing star, brittle star, electric car, elevator car, evening star, feather star, hitching bar, iceland spar, libyan dinar, morning star, neutron star, prairie star, railroad car, serpent star, sleeping car, steel guitar, that you are, vina del mar, wrecking bar, yemeni dinar

13 letters:
and there are, bahrain dinar, beluga caviar, chocolate bar, conservatoire, cote d'ivoire, devil's cigar, iranian dinar, kuwaiti dinar, multiple star, operatic star, passenger car, shooting star, variable star, weather radar, woodland star

14 letters:
algerian dinar, amphiprostylar, christmas star, greenland spar, horizontal bar, jewels-of-opar, nonsmoking car, red dwarf star, tunisian dinar, white feldspar

15 letters:
acoustic guitar, earthenware jar, electric guitar, hawaiian guitar, jordanian dinar, microwave radar, television star

16 letters:
air search radar, capital of qatar, refrigerator car, white dwarf star

17 letters:
yugoslavian dinar

18 letters:
dense blazing star, fire control radar

19 letters:
early warning radar, political commissar

20 letters:
surface search radar

21 letters:
southern yemeni dinar

2 letters:
or, er

3 letters:
bur, mir, for, air, fur, war, err, oar, ore, ear, ayr, tor, sir, ire, cur, nor, per, fir

4 letters:
deer, bear, pare, lore, more, sour, slur, dare, poor, lour, gore, torr, rear, door, wear, weir, bore, fair, year, tyre, amir, dire, boer, veer, were, gear, hire, boar, hare, lear, core, hour, lair, boor, near, sore, tier, sure, mare, jeer, yore, pair, wore, pore, soar, moor, hair, sear, meir, cure, fare, four, herr, doer, fear, fore, tear, your, bier, care, burr, fire, wire, pour, rare, dour, bare, blur, birr, lyre, tore, hear, sere, ware, mire, beer, spur, emir, dear, pure, ruhr, hoar, seer, lure, mere, thor, purr, heir, pear, peer, stir, here, tour, roar, pier, abor, fehr, gere, igor, jour, lohr

5 letters:
khmer, score, loire, aware, blair, moore, assur, whore, crore, churr, queer, snore, skier, glare, blare, ameer, drear, ne'er, whirr, flair, chore, scour, defer, cheer, flare, afire, store, amour, spore, dower, senor, demur, steer, corps, share, shirr, stair, we're, there, snare, chirr, stare, inure, shore, floor, myrrh, spear, their, sneer, quire, inter, shear, swear, adore, spare, abhor, incur, shire, sheer, chair, flour, zaire, spoor, occur, refer, scare, blear, clear, moire, infer, deter, spire, smear, decor, murre, swore, recur, where, ashir, astir, freyr, greer, grier, sapir, sherr, vanir, yasir

6 letters:
appear, unfair, impure, secure, velour, impair, insure, drawer, career, confer, sphere, midair, ensure, affair, assure, square, immure, aspire, adjure, galore, pierre, vigour, endear, unsure, endure, ignore, squire, retire, beware, concur, rehear, repair, prayer, tumour, cohere, valour, severe, claire, prewar, detour, mature, go for, before, poseur, ashore, vapour, prefer, manure, you're, veneer, demure, revere, adhere, savour, voyeur, allure, admire, expire, abjure, aflare, eclair, exmoor, fakeer, inhere, kaffir, lenore, menhir, o'hare, pindar, rigour, safire, salvor, sambur, schorr, shamir, shmear

7 letters:
ask for, austere, compere, verdure, hot air, big sur, respire, rapport, pasteur, hot war, pay for, compare, unclear, inshore, liqueur, premier, anymore, prepare, schmear, require, deplore, pioneer, they're, inquire, postwar, saviour, masseur, cashier, inspire, sincere, restore, couture, ensnare, declare, compeer, au pair, danseur, succour, de jure, obscure, unaware, fervour, procure, explore, flavour, affaire, despair, implore, astaire, besmear, bonaire, bonheur, bugbear, cooccur, cry for, flexure, forbear, gravure, guinier, hachure, houhere, kildeer, languor, moliere, nervure, no more, on tour, opt for, outroar, rancour, run for, soilure, tangier, tarsier, tonsure, try for, tussore, upstair, up here, wafture

8 letters:
brochure, overhear, look for, call for, polypore, reappear, brumaire, engineer, send for, reinsure, boer war, seigneur, red deer, souvenir, what for, low gear, cavalier, offshore, due care, saboteur, mutineer, day care, frontier, frotteur, lead ore, ant bear, grandeur, immature, fall for, domineer, frimaire, open air, voltaire, roe deer, monsieur, care for, sea hare, reassure, for sure, debonair, forswear, premiere, perspire, done for, transfer, cold war, abampere, allosaur, amanpour, barosaur, blue air, bus fare, cab fare, calm air, car care, car door, cat bear, coiffeur, coiffure, coinsure, derriere, elaphure, encolure, ex-mayor, feel for, fend for, footgear, footsure, give ear, got your, handwear, hot-wire, ice bear, iron ore, killdeer, lavalier, longueur, make for, markhoor, muleteer, open-air, outscore, overbear, paramour, parterre, per year, put your, sinecure, sun gear, t-square, take for, tamanoir, testiere, true fir, twoscore, wheatear, wirehair

9 letters:
balladeer, guarantor, leap year, buccaneer, puppeteer, fire door, light air, bock beer, life peer, great war, price war, chevalier, raconteur, disappear, inner ear, speak for, joint fir, solitaire, mouse ear, next door, trap door, insincere, musketeer, all clear, back door, holy year, persevere, musk deer, root beer, near beer, premature, gondolier, root hair, volunteer, world war, civil war, profiteer, spur gear, disrepair, cold sore, barn door, interfere, pap smear, stand for, take care, bandolier, racketeer, sightseer, chauffeur, financier, brigadier, outer ear, mule deer, high gear, skin care, worm gear, belvedere, make sure, wild boar, open door, air corps, allow for, apatosaur, archosaur, bandoleer, basketeer, cafe noir, cannoneer, cared-for, chinaware, class war, come near, coon bear, cover for, dark beer, debonaire, downstair, draw near, duty tour, each year, fourscore, gadgeteer, gazetteer, giant fir, give care, go to war, grand fir, grope for, guinevere, gum myrrh, hadrosaur, hair care, half door, held dear, hold dear, hoped-for, horsehair, make pure, megathere, nothosaur, once more, over here, pistoleer, plump for, plunk for, presbyter, privateer, pterosaur, pushchair, quest for, red scare, rest-cure, set afire, shoot for, side door, sloganeer, sonneteer, sorry for, stegosaur, stud mare, sweep oar, taxi fare, that your, trochlear, warrantor, wasteweir, white fir

10 letters:
quadrature, answer for, small beer, great bear, pinot noir, bombardier, first gear, honey bear, try square, chandelier, charioteer, korean war, light year, liquid air, tidal bore, bevel gear, bath chair, commandeer, front door, louis d'or, lawn chair, black bear, pubic hair, dutch door, lunar year, middle ear, solar year, in the air, mal de mer, set square, polar bear, deck chair, side chair, foursquare, underscore, balsam fir, child care, heretofore, swing door, shop floor, trojan war, easy chair, petit four, civil year, guard hair, brown bear, great year, silver fir, auctioneer, stage door, grand tour, wing chair, teddy bear, koala bear, mouse deer, air-to-air, alpine fir, ankylosaur, baudelaire, bear's ear, birch beer, blackamoor, brontosaur, budget for, burro deer, called for, camp chair, carabineer, ceratosaur, cockleburr, cross hair, debonnaire, embouchure, every year, faith cure, false hair, fraser fir, god of war, gondoliere, great care, ground fir, halberdier, harpooneer, ictodosaur, in one ear, kieselguhr, light beer, longed-for, looked-for, man-of-war, marsh hare, mens store, mouse hare, oregon fir, panda bear, pelycosaur, plesiosaur, polar hare, re-explore, river pear, scotch fir, scrutineer, secretaire, seismosaur, set ashore, shoe store, skunk bear, sloth bear, smoothbore, swamp hare, third gear, threescore, to be sure, to one ear, train fare, tug-of-war, uintathere, water deer, weiss beer, wished-for, woody pear

11 letters:
saddle sore, apgar score, word square, bronx cheer, kodiak bear, pamphleteer, fallow deer, crimean war, uncared-for, billionaire, school year, woolly bear, spruce beer, ginger beer, litterateur, doctrinaire, dental care, first floor, dance floor, sedan chair, millionaire, little bear, solar flare, edward lear, connoisseur, candy store, love affair, peace corps, common year, rectilinear, limited war, screen door, ichthyosaur, account for, health care, vanity fair, interlinear, douglas fir, balsam pear, mexican war, potty chair, vietnam war, fiscal year, french door, flying mare, six day war, arctic hare, beach chair, black maire, buffalo bur, camera care, candidature, church year, come before, come in for, corythosaur, cry out for, death chair, double door, dressed ore, dromaeosaur, gala affair, gomphothere, looking for, lowland fir, milliampere, munich beer, native bear, native pear, ocean floor, peacock ore, planet gear, prepare for, press corps, provide for, puff of air, rotogravure, schenk beer, seckel pear, second gear, slight care, spanish war, squeeze for, stable gear, styracosaur, subway fare, supersedure, syrian bear, take a dare, that you're, tyrannosaur, unhoped-for, uranium ore, volt-ampere, walk on air, what's your, what you're, white maire, wicket door, yacht chair, yearned-for

12 letters:
morris chair, barking deer, bill of fare, camel's hair, ground floor, magic square, folding door, landing gear, state of war, grizzly bear, internal ear, entrepreneur, belgian hare, times square, white squire, bevel square, external ear, prickly pear, sloop of war, kuala lumpur, marine corps, elephant ear, liquor store, anchovy pear, swivel chair, avocado pear, green manure, latin square, restaurateur, soup du jour, barber chair, bartle frere, buffer store, ceramic ware, colorado fir, far and near, fishing gear, flower store, garden chair, going ashore, head of hair, heliogravure, in disrepair, king's spear, leisure wear, lounge chair, marston moor, medical care, nursing care, outside door, photogravure, pied-a-terre, powder store, psittacosaur, retail store, savoir-faire, sensory hair, service door, sliding door, standing for, staurikosaur, time of year, uncalled-for, unlooked-for, unwished-for, varying hare, what is more, without fear

13 letters:
virginia deer, nom de guerre, lord's prayer, wear and tear, laissez faire, snowshoe hare, calendar year, louis pasteur, questionnaire, haute couture, academic year, steering gear, crystal clear, rocking chair, general store, cinnamon bear, package store, force majeure, conventioneer, rouge et noir, tropical year, windsor chair, grocery store, army engineer, bartlett pear, bowling score, bring to bear, carte du jour, country store, european hare, exterior door, feeding chair, folding chair, hospital care, interior door, japanese deer, jewelry store, kangaroo bear, kangaroo hare, laissez-faire, last frontier, market square, more and more, musical score, ordinary care, oriental sore, parquet floor, platonic year, porte-cochere, porter's beer, public square, social affair, stinging hair, swinging door, tropical sore

14 letters:
evening prayer, financial year, civil engineer, planetary gear, alligator pear, hardware store, concessionaire, discount store, morning prayer, cervical smear, compressed air, walking on air, electric chair, accordion door, baseball score, christian year, clothing store, coffee liqueur, commissionaire, computer store, elephant's ear, football score, hold still for, know the score, legal transfer, naval engineer, orange liqueur, pneumatic tyre, red silver fir, straight chair, surface-to-air, take the floor, warning of war, war to end war, whitetail deer, white lead ore, world premiere, yom kippur war

15 letters:
croix de guerre, first world war, cauliflower ear, sabbatical year, black marketeer, flight engineer, prisoner of war, esprit de corps, reasonable care, captain's chair, have been there, house of prayer, jewish new year, kilovolt-ampere, marine engineer, mezzanine floor, mining engineer, out of thin air, reclining chair, responsible for, santa lucia fir, specialty store, us marine corps, with great care

16 letters:
second world war, celestial sphere, department store, diplomatic corps, basketball score, capital of zaire, come to the fore, highway engineer, on a lower floor, pachycephalosaur, pays de la loire, persian gulf war, political sphere, secretary of war, seven years' war, step to the fore

17 letters:
astronomical year, differential gear, thirty years' war, convenience store, peloponnesian war, castle in the air, brace oneself for, earning per share, english civil war, green douglas fir, implements of war, little chief hare, lowland white fir, military engineer, on a higher floor, overstuffed chair, pere david's deer, railroad engineer, software engineer

18 letters:
hundred years' war, american civil war, aerospace engineer, alaskan brown bear, carpenter's square, haberdashery store, military volunteer, pacific silver fir, russo-japanese war, tender loving care

19 letters:
mechanical engineer, electrical engineer, american black bear, automotive engineer, efficiency engineer, elasticity of shear, european silver fir, franco-prussian war

20 letters:
california white fir, pinion and ring gear, vestibule of the ear

21 letters:
delusions of grandeur, book of common prayer, aeronautical engineer, building supply store, french and indian war, inspection and repair

22 letters:
battle of marston moor, metallurgical engineer, privilege of the floor

31 letters:
reserve officers training corps