2 letters:
or

3 letters:
cor, for, mor, nor, oar, ore, orr, por, tor, war

4 letters:
abor, boar, boer, bohr, bore, core, corr, dior, door, dorr, flor, fore, four, gore, hoar, igor, lohr, lore, more, pore, pour, roar, saur, soar, sore, thor, tore, torr, wore, yore, your

5 letters:
abhor, adore, afore, angor, chlor, chore, corps, crore, decor, floor, fomor, frore, gabor, moore, score, senor, shore, smore, snore, spore, store, swore, timor, whore

6 letters:
and/or, ardour, ashore, bangor, before, bezoar, chador, drawer, encore, galore, go for, ignore, indoor, inocor, lahore, lenore, mentor, mysore, prewar, salvor, schorr, uproar, vapour

7 letters:
anymore, ask for, bedsore, candour, centaur, cry for, deplore, ecuador, explore, eyesore, hot war, humidor, implore, inshore, languor, matador, mevacor, mirador, moidore, no more, onshore, opt for, outdoor, outpour, outroar, pay for, picador, pledgor, postwar, rapport, restore, run for, tandoor, try for, tussore

8 letters:
albacore, allosaur, backdoor, barndoor, barosaur, boer war, call for, care for, car door, claymore, cold war, dinosaur, done for, evermore, ex-mayor, fall for, feel for, fend for, folklore, footsore, forswore, got your, hardcore, iron ore, labrador, lead ore, look for, make for, minotaur, offshore, outscore, phosphor, pinafore, polypore, put your, seashore, send for, sycamore, take for, theodore, therefor, trapdoor, twoscore, unprofor, what for, wherefor, zoospore

9 letters:
air corps, allow for, apatosaur, archosaur, back door, baltimore, bangalore, barn door, barrymore, bookstore, bucentaur, cared-for, carnivore, carnosaur, civil war, class war, cold sore, commodore, comprador, cover for, drugstore, embraceor, fire door, foreshore, fourscore, frugivore, go to war, great war, grope for, guarantor, hackamore, hadrosaur, half door, hard-core, herbivore, hoped-for, lakeshore, livermore, longshore, madrepore, manticore, nevermore, next door, nothosaur, once more, open door, plump for, plunk for, price war, pterosaur, quest for, shoot for, side door, singapore, soft-core, sophomore, sorry for, speak for, splendour, stand for, stegosaur, stevedore, sweep oar, that your, therefore, thermidor, trap door, warrantor, wherefore, wild boar, world war

10 letters:
alongshore, ankylosaur, answer for, apishamore, battledore, blastopore, brontosaur, budget for, called for, ceratosaur, dutch door, front door, god of war, heretofore, ictodosaur, korean war, longed-for, looked-for, louis d'or, man-of-war, megalosaur, mens store, pelycosaur, petit four, pisanosaur, plesiosaur, re-explore, seismosaur, set ashore, shoe store, shop floor, smoothbore, stage door, superstore, swing door, threescore, tidal bore, titanosaur, trojan war, troubadour, tug-of-war, underscore, wished-for

11 letters:
account for, apgar score, candy store, closed-door, come before, come in for, corythosaur, crimean war, cry out for, dance floor, double door, dressed ore, dromaeosaur, first floor, forevermore, french door, furthermore, herrerasaur, ichthyosaur, kinetochore, limited war, looking for, mexican war, ocean floor, out-of-door, peace corps, peacock ore, prepare for, press corps, provide for, saddle sore, screen door, six day war, spanish war, squeeze for, styracosaur, theretofore, the centaur, twenty-four, two-by-four, tyrannosaur, uncared-for, unhoped-for, uranium ore, vietnam war, what's your, wicket door, yearned-for

12 letters:
buffer store, conquistador, door-to-door, flower store, folding door, going ashore, ground floor, hereinbefore, liquor store, marine corps, outside door, powder store, psittacosaur, retail store, service door, sliding door, sloop of war, standing for, state of war, staurikosaur, trichobezoar, uncalled-for, unlooked-for, unwished-for, what is more

13 letters:
argentinosaur, bowling score, country store, exterior door, general store, grocery store, interior door, jewelry store, more and more, musical score, oriental sore, package store, parquet floor, swinging door, tropical sore

14 letters:
accordion door, baseball score, circumferentor, clothing store, coach-and-four, computer store, discount store, football score, green dinosaur, hardware store, hold still for, know the score, take the floor, warning of war, war to end war, white lead ore, yom kippur war

15 letters:
esprit de corps, first world war, horned dinosaur, mezzanine floor, prisoner of war, responsible for, specialty store, us marine corps, young carnivore

16 letters:
arizona sycamore, armored dinosaur, basketball score, come to the fore, department store, diplomatic corps, on a lower floor, pachycephalosaur, persian gulf war, second world war, secretary of war, seven years' war, step to the fore

17 letters:
american sycamore, brace oneself for, convenience store, english civil war, implements of war, on a higher floor, peloponnesian war, thirty years' war

18 letters:
american civil war, capital of ecuador, haberdashery store, hundred years' war, russo-japanese war

19 letters:
california sycamore, franco-prussian war

20 letters:
capital of singapore

21 letters:
building supply store, french and indian war

22 letters:
privilege of the floor

31 letters:
reserve officers training corps

6 letters:
acinar, avatar, acular

7 letters:
rattler, aquifer, manager, samovar, tanager, amateur, papaver, saddler, annular, handler, basilar, wagoner, caliber, jacamar, malodor, palaver, angular, caliper, janitor, battler, dabbler, paddler

8 letters:
balancer, canister, bachelor, lavender, prattler, scapular, traveler, vascular, fastener, diameter, ampullar, granular, cavalier, wrangler, catheter, calendar, cannular, examiner, falconer, massacre, waggoner, baluster, zanzibar, oracular, adductor, cadastre, calender, vladimir

9 letters:
avascular, cannoneer, glandular, traveller, handlebar, lancaster, bannister, sapsucker, scavenger, capacitor, absconder, decameter, parameter, excalibur, canvasser, bandoleer, passenger, gadgeteer, phalanger, tablature, decaliter, elastomer, dekameter, kala-azar, agateware, blastular, camelhair, dekalitre, gallagher, handcolor, hexameter, octameter

10 letters:
enamelware, lacklustre, ambassador, chancellor, embassador, atmosphere, landlubber, clawhammer, enantiomer, vernacular, triangular, acetabular, challenger, blackamoor, lackluster, blastomere, blasphemer, hexangular, lapplander, octangular, pentameter, saltshaker

11 letters:
crackleware, spectacular, rectangular, grandmother, gametophore, pentangular, straphanger, entablature, graniteware

12 letters:
peradventure, city manager, half-brother, milliammeter, sea lavender, blastosphere, stratosphere, semidiameter, zip-fastener

13 letters:
stage manager, snap fastener, bank examiner, hotel manager, sash fastener

14 letters:
slide fastener, spike lavender, cardiovascular, hindu calendar, roman calendar, cross-examiner, ground rattler, horse wrangler, lunar calendar, paper fastener, solar calendar, world traveler

15 letters:
julian calendar, vernier caliper, jewish calendar, lord chancellor, knight bachelor, fellow traveler, vice chancellor, church calendar, french lavender, general manager, hebrew calendar, iron chancellor, like an amateur, moslem calendar, muslim calendar, prairie rattler

16 letters:
medical examiner, bypass capacitor, district manager, english lavender, fellow traveller, hearing examiner

17 letters:
great grandmother, business traveler, farmer's calendar

18 letters:
gregorian calendar, micrometer caliper, trimming capacitor

19 letters:
commercial traveler, corrugated fastener

20 letters:
appointment calendar, commercial traveller, lord high chancellor

22 letters:
electrolytic capacitor, revolutionary calendar

23 letters:
ecclesiastical calendar

24 letters:
black english vernacular