3 letters:
orn

4 letters:
born, corn, dorn, horn, korn, morn, orne, porn, torn, warn, worn, zorn

5 letters:
-born, aborn, adorn, anorn, awarn, bjorn, borne, bourn, corne, doorn, frorn, horne, lorne, mourn, quorn, scorn, shorn, sporn, sworn, thorn, torne, yourn

6 letters:
-borne, alcorn, amborn, bjoern, boerne, bourne, inborn, itworn, mourne, noforn, osborn, reborn, schorn, suborn, thorne, tomorn, unborn

7 letters:
airborn, allcorn, aragorn, bemourn, be born, bighorn, diswarn, eggcorn, einhorn, elkhorn, forlorn, lamborn, lowborn, osborne, outworn, parforn, pibgorn, popcorn, preborn, prewarn, redhorn, runcorn, sanborn, skywarn, tinhorn, unadorn, unicorn, unshorn, unsworn, upborne, vandorn, vanhorn, wanhorn, warworn, wayworn, youporn

8 letters:
airborne, amelcorn, avercorn, bluhdorn, buckhorn, bullhorn, careworn, car horn, dearborn, disadorn, eekhoorn, fairborn, feedhorn, findhorn, forborne, forewarn, foreworn, forsworn, gisborne, gunicorn, hawthorn, hegadorn, jetborne, kilborne, lasslorn, lastborn, layborne, longhorn, low-born, mageborn, mangcorn, metecorn, mindhorn, mistborn, mongcorn, mungcorn, nordhorn, o'diorne, outscorn, pangborn, radborne, sea-born, seaborne, shoehorn, shopkorn, shopworn, taxicorn, terkhorn, timeworn, toilworn, trueborn, vanhorne, waldhorn, war-worn, waveworn, wellborn, whithorn

9 letters:
apeldoorn, ashbourne, base-born, bass horn, broomcorn, buckthorn, city-born, crowsworn, crow corn, cyberporn, dead-born, dent corn, firstborn, foodborne, fool-born, foresworn, hartshorn, heliborne, high-born, hirshhorn, last-born, mclawhorn, neushoorn, oceanborn, paderborn, pile-worn, plenicorn, post horn, pronghorn, seed corn, self-born, sigh-born, soft corn, steinborn, stillborn, stockhorn, stormborn, time-worn, true-born, ward-corn, wave-worn, well-born, wendehorn, whitehorn, windborne

10 letters:
barleycorn, blackthorn, bloodborne, broom-corn, candy corn, chairborne, dragonborn, earth-born, field corn, fire thorn, first-born, fishbourne, flint corn, flour corn, green corn, legendborn, manglehorn, motor horn, oudtshoorn, peppercorn, quickthorn, romanshorn, sirindhorn, still-born, still/born, sugar corn, sweet corn, tick-borne, twice-born, water-worn, waterborne, wind-borne

11 letters:
allalinhorn, barley-corn, basset horn, blood-borne, edible corn, french horn, girlsdoporn, guinea corn, hedge thorn, indian corn, lamellicorn, little horn, native-born, otterbourne, pepper-corn, pfefferkorn, polkinghorn, powder horn, schoellhorn, shard-borne, tooth-borne, trevor horn, water-borne, yankee corn

12 letters:
bella thorne, christ thorn, english horn, foreign-born, glyndebourne, natural-born, rhea seehorn, spindle horn, straighthorn, winterbourne

13 letters:
baritone horn, chulalongkorn, egyptian corn, jesus is born, pear hawthorn, squirrel corn

14 letters:
little bighorn, texas longhorn, vajiralongkorn

15 letters:
alder buckthorn, automobile horn, evergreen thorn, false buckthorn, jerusalem thorn, virtualrealporn

16 letters:
english hawthorn

18 letters:
carolina buckthorn, golden age of porn, jeanne tripplehorn, southern buckthorn

20 letters:
california buckthorn

21 letters:
johnny english reborn

22 letters:
rocky mountain bighorn

24 letters:
battle of little bighorn

28 letters:
battle of the little bighorn

29 letters:
naked as the day one was born

30 letters:
naked as the day you were born

3 letters:
urn

4 letters:
bern, turn, darn, erne, yarn, fern, kern, barn, burn, earn

5 letters:
stern, bairn, cairn, learn, berne, spurn, yearn, quern, churn, byrne

6 letters:
return, unworn, upturn, attorn, edirne, casern, extern, secern

7 letters:
in turn, discern, adjourn, unlearn, concern, cowbarn, interne, relearn, tea urn

8 letters:
sauterne, cow barn, fan fern, ill turn, lip fern, o'beirne, oak fern

9 letters:
seed fern, unconcern, good turn, spun yarn, stem turn, rope yarn, kick turn, tree fern, male fern, ball fern, bead fern, deer fern, felt fern, film fern, gold fern, hand fern, hard fern, in return, king fern, lace fern, lady fern, pine fern, rasp fern, rope burn, sago fern, wall fern, wood-fern, wood fern

10 letters:
royal fern, tax return, sword fern, beech fern, about turn, sweet fern, day return, berry fern, chain fern, coffee urn, crepe fern, ditch fern, giant fern, glade fern, glory fern, grape fern, grass fern, holly fern, horse barn, marsh fern, scale fern, snake fern, strap fern, tithe barn, water fern, whisk fern, winter urn

11 letters:
boston fern, annual fern, bamboo fern, basket fern, button fern, clover fern, coffee fern, dagger fern, devil's urn, golden fern, jersey fern, kidney fern, meadow fern, potato fern, ribbon fern, shield fern, silver fern, spider fern, tongue fern, winter fern

12 letters:
joint return, walking fern, aquatic fern, bladder fern, boulder fern, bristle fern, brittle fern, buckler fern, butter churn, elkhorn fern, false return, fragile fern, leather fern, ostrich fern, scented fern, self-concern, serpent fern, with concern

13 letters:
climbing fern, cinnamon fern, creeping fern, floating fern, hartford fern, licorice fern, mosquito fern, mountain fern, nebraska fern, new york fern, oleander fern, umbrella fern

14 letters:
amended return, asparagus fern, christmas fern, cigarette burn, flowering fern, hairy lip fern, limestone fern, sensitive fern, soft tree fern, wooly lip fern

15 letters:
chili con carne, carriage return, banking concern, black tree fern, california fern, earthly concern, long beech fern, pay as you earn, smooth lip fern, without concern, worldly concern

16 letters:
alabama lip fern, alpine lady fern, bird's nest fern, broad beech fern, business concern, curly grass fern, interrupted fern, printing concern, rattlesnake fern, silver tree fern, soft shield fern

17 letters:
income tax return, narrow beech fern, northern oak fern, packaging concern, resurrection fern

18 letters:
point of no return, american wall fern, braun's holly fern, carolina pond fern, exponential return, florida strap fern, fragrant wood fern, indian button fern, information return, marginal wood fern, massachusetts fern, mountain male fern, skeleton fork fern, toothed sword fern, western holly fern

19 letters:
evergreen wood fern, fragrant cliff fern, leathery grape fern, northern beech fern, northern holly fern, prickly shield fern, southern beech fern, virginia chain fern

20 letters:
brittle bladder fern, estimated tax return, fragrant shield fern

21 letters:
american parsley fern, european parsley fern, giant scrambling fern, mountain bladder fern, mountain parsley fern, southwestern lip fern

25 letters:
climbing bird's nest fern

27 letters:
central american strap fern

30 letters:
canary island hare's foot fern