2 letters:
er, ur

3 letters:
bir, bur, cur, der, fer, fir, fur, her, hur, ker, per, pur, sir, sur, ter, ver, yer

4 letters:
birr, blur, burr, dirr, duhr, durr, eure, feur, furr, gurr, jerr, kerr, kuhr, luhr, murr, nurr, pere, purr, sher, shir, shur, slur, spur, stir, swor, thur, were

5 letters:
-ster, -word, chier, chir-, chirr, churr, chvre, cirrh, clbre, cofer, defer, demur, deter, dufur, excur, ferr-, fhrer, flere, fleur, fluhr, furrh, hksar, icurr, incur, infer, inter, jagir, jstor, k-lor, klear, kshmr, mccur, mller, mugir, murre, myrrh, nurre, occur, odeur, pdf/a, phore, plurr, prtor, pter-, purre, recur, refer, rmdir, robur, scher, schur, scler, shirr, shurr, sieur, sigir, skirr, smirr, spher, spurr, squir, stirr, stuhr, tl;dr, twere, ungir, we're, whirr

6 letters:
-phore, ampere, ardeur, b-word, boxeur, c-word, chirre, concur, confer, diseur, erreur, esquer, f-word, faveur, fiverr, flneur, fumeur, humeur, joueur, k-word, mcgirr, mineur, mnster, mushir, myrrhe, n-word, naveur, oclair, osburh, payeur, phthor, poseur, prefer, r-word, s-word, sambur, saveur, schnur, schurr, schwer, schwur, sf ber, sklere, squirr, teneur, tozeur, tumeur, upstir, vapeur, videur, viveur

7 letters:
adoucir, amateur, asistir, big sur, bonheur, brisure, broyeur, by-word, campeur, causeur, censeur, chembur, commere, cooccur, craseur, credeur, curseur, danseur, defleur, demeure, existir, flaneur, friseur, frisure, graveur, honneur, horreur, jt thor, lafleur, largeur, lefleur, liqueur, malheur, o'clair, orateur, preneur, primeur, ramseur, ranseur, redifer, reincur, reoccur, rongeur, schnurr, schreur, serveur, stupeur, tampere, telesur, terreur, tiqueur, wh-word

8 letters:
affineur, arroseur, assureur, butineur, chanteur, charmeur, chesshir, claqueur, co-occur, coiffeur, desistir, diviseur, donateur, dpanneur, ecraseur, el-aksur, froideur, geschirr, harfleur, honfleur, insistir, investir, larkspur, longspur, longueur, manastir, marqueur, mercosur, monastir, monsieur, mtmc eur, nilambur, overwore, plongeur, predecir, puanteur, ramoneur, rgisseur, saboteur, sam kerr, scanneur, seigneur, shamshir, siffleur, silencer, soigneur, tourneur, transfer, trouveur, true fir, usnaveur, voyageur

9 letters:
arrangeur, ascenseur, atomiseur, bagarreur, bill burr, cascadeur, cbt sttar, chauffeur, code-word, coexistir, conteneur, depanneur, escrimeur, fondateur, francoeur, giant fir, grand fir, gum myrrh, imprimeur, ingenieur, joint-fir, joint fir, operateur, pass-word, persistir, procureur, prosateur, radiateur, regisseur, renifleur, schnuller, shamateur, shuldiner, souffleur, souteneur, vainqueur, voltigeur, whisperer, white fir

10 letters:
adaptateur, admirateur, alpine fir, armbanduhr, aspirateur, balsam fir, bellefleur, brocanteur, brunanburh, camionneur, camoufleur, catalyseur, catch-word, chou-fleur, cockleburr, courmayeur, derbyshire, fraischeur, fraser fir, gouverneur, ground fir, kieselguhr, littrateur, migraineur, millefleur, mompreneur, nonce-word, ordinateur, oregon fir, persifleur, raisonneur, randonneur, scotch fir, silver fir, summerstir, topinambur, wetransfer

11 letters:
alternateur, ambassadeur, autocuiseur, buffalo bur, calculateur, carburateur, chikmagalur, chroniqueur, cockle-burr, connaisseur, connoisseur, dessinateur, dimmuborgir, douglas fir, entrepeneur, explorateur, hypnotiseur, infopreneur, kodungallur, litterateur, lowland fir, monseigneur, nanganallur, programmeur, spoken-word

12 letters:
accumulateur, additionneur, adichanallur, carillonneur, colorado fir, entrepreneur, intrapreneur, restaurateur

13 letters:
collaborateur, entreupreneur, macos big sur, michael schur, mv derbyshire, restauranteur, technopreneur, word-for-word

14 letters:
coffee liqueur, collectionneur, conglomerateur, legal transfer, orange liqueur, red silver fir, sholinganallur

15 letters:
croque-monsieur, like an amateur, rocket larkspur, santa lucia fir

17 letters:
green douglas fir, lowland white fir

18 letters:
pacific silver fir

19 letters:
european silver fir

20 letters:
california white fir

2 letters:
ar, or

3 letters:
for, jar, npr, air, par, mar, war, err, far, oar, ore, gar, ear, car, ayr, tor, are, ire, nor, bar, tar

4 letters:
bear, pare, lore, more, sour, dare, poor, lour, gore, torr, door, wear, bore, weir, fair, tyre, dire, boer, spar, hire, boar, hare, core, hour, star, lair, boor, sore, tier, sure, mare, yore, pair, wore, pore, soar, moor, hair, cure, fare, four, herr, doer, fore, carr, scar, your, bier, parr, care, fire, czar, wire, pour, rare, dour, bare, tsar, lyre, tore, hear, ware, mire, char, pure, ruhr, hoar, seer, lure, thor, heir, pear, here, tour, roar, barr, adar

5 letters:
khmer, score, loire, aware, blair, moore, assur, barre, whore, crore, snore, skier, glare, blare, sitar, ne'er, qatar, flair, chore, scour, flare, afire, store, amour, spore, dower, senor, safar, corps, share, babar, stair, unbar, there, snare, stare, inure, shore, floor, their, quire, swear, adore, spare, dakar, abhor, shire, dinar, bazar, chair, flour, spoor, scare, starr, moire, spire, decor, swore, where, cigar

6 letters:
lekvar, unfair, impure, secure, velour, impair, insure, guitar, drawer, midair, ensure, affair, assure, square, immure, bazaar, aspire, adjure, galore, so far, pierre, vigour, endear, disbar, unsure, endure, ignore, squire, retire, beware, rehear, repair, prayer, tumour, valour, claire, prewar, detour, mature, go for, before, qintar, ashore, vapour, manure, you're, demure, savour, voyeur, allure, admire, by far, expire

7 letters:
ask for, verdure, hot air, myanmar, respire, rapport, pasteur, hot war, pay for, compare, inshore, anymore, prepare, require, deplore, they're, inquire, postwar, saviour, masseur, inspire, restore, bizarre, couture, ensnare, declare, au pair, succour, de jure, obscure, unaware, fervour, procure, explore, flavour, affaire, despair, wet bar, implore

8 letters:
brochure, grimoire, overhear, look for, call for, nightjar, sea star, polypore, brumaire, send for, reinsure, boer war, milk bar, what for, tank car, offshore, due care, day care, wood tar, frotteur, dog star, lead ore, ant bear, grandeur, immature, fall for, pace car, frimaire, bell jar, open air, voltaire, care for, sea hare, coal tar, reassure, for sure, debonair, forswear, cash bar, perspire, done for, pine tar, sand bar, cold war

9 letters:
guarantor, buccaneer, blue star, rock star, puppeteer, fire door, candy bar, light air, stock car, superstar, great war, price war, snack bar, raconteur, speak for, solitaire, squad car, trap door, musketeer, back door, salad bar, premature, root hair, world war, civil war, color bar, disrepair, pinch bar, cold sore, barn door, space bar, stand for, cable car, take care, sightseer, au revoir, skin care, film star, make sure, wild boar, mason jar, open door, next door

10 letters:
quadrature, answer for, great bear, buffet car, polar star, pinot noir, flare star, honey bear, cookie jar, racing car, try square, bumper car, double bar, korean war, liquid air, leyden jar, tidal bore, bath chair, north star, escritoire, front door, louis d'or, lawn chair, black bear, pubic hair, dutch door, in the air, mal de mer, set square, dining car, polar bear, deck chair, side chair, foursquare, underscore, sports car, heavy spar, child care, heretofore, swing door, shop floor, trojan war, easy chair, petit four, movie star, patrol car, guard hair, brown bear, giant star, police car, stage door, fixed star, grand tour, estate car, wing chair, teddy bear, koala bear, parlor car

11 letters:
freight car, baggage car, saddle sore, apgar score, word square, binary star, kodiak bear, trolley car, crimean war, uncared-for, gondola car, billionaire, woolly bear, doctrinaire, dental care, first floor, dance floor, sedan chair, millionaire, little bear, solar flare, candy store, love affair, silver star, peace corps, bronze star, arctic char, limited war, screen door, ichthyosaur, account for, health care, vanity fair, balsam pear, mexican war, potty chair, basket star, double star, vietnam war, french door, flying mare, six day war, touring car

12 letters:
morris chair, evening star, sleeping car, bill of fare, morning star, blazing star, wrecking bar, camel's hair, ground floor, magic square, folding door, feather star, state of war, grizzly bear, iceland spar, belgian hare, times square, white squire, bevel square, neutron star, prickly pear, sloop of war, steel guitar, brittle star, kuala lumpur, marine corps, liquor store, anchovy pear, swivel chair, avocado pear, green manure, latin square, soup du jour

13 letters:
nom de guerre, lord's prayer, wear and tear, laissez faire, multiple star, snowshoe hare, louis pasteur, questionnaire, haute couture, passenger car, rocking chair, general store, cinnamon bear, package store, force majeure, rouge et noir, variable star, shooting star, windsor chair, grocery store

14 letters:
evening prayer, alligator pear, hardware store, concessionaire, discount store, morning prayer, compressed air, horizontal bar, walking on air, electric chair

15 letters:
hawaiian guitar, croix de guerre, first world war, acoustic guitar, prisoner of war, esprit de corps, electric guitar, reasonable care

16 letters:
second world war, department store, diplomatic corps

17 letters:
thirty years' war, convenience store, peloponnesian war, castle in the air

18 letters:
hundred years' war, american civil war

21 letters:
delusions of grandeur, book of common prayer