2 letters:
ed

3 letters:
bed, fed, ged, jed, led, med, ned, red, ted, wed, zed

4 letters:
abed, bled, bred, coed, dead, dred, fled, fred, head, lead, nedd, pled, read, redd, said, shed, sled, sped, swed, wedd

5 letters:
-head, ahead, amedd, anred, bread, dread, dredd, embed, fread, freda, guede, imbed, kaede, nsaid, nsted, numed, oread, reade, redde, sayed, sched, sffed, shaed, shead, shedd, shred, sledd, stead, szwed, tread, unfed, unted, unwed, wedde, wehde

6 letters:
addend, adread, anrede, ausaid, behead, biomed, boobed, calfed, colead, comfed, con-ed, confed, delmed, gisaid, hotbed, inbred, kerfed, lamedh, manred, misled, miswed, moshed, nedved, oramed, oxhead, premed, schwed, scimed, seabed, senedd, spread, sunbed, thread, unbred, undead, unhead, unlead, unread, unsaid, viread, vivaed

7 letters:
airhead, anstead, ax head, baghead, bedhead, bighead, bobsled, bowhead, boxhead, cathead, cityfed, cornfed, cuphead, day bed, dechead, duramed, egghead, embread, enisled, fathead, flatbed, glenfed, godhead, gorsedd, gwynedd, homefed, hophead, hothead, hungred, instead, jarhead, jughead, lawhead, lipread, lowbred, manhead, misread, mophead, mudhead, netdead, nethead, onstead, ore bed, ounsted, overfed, panhead, peghead, pig bed, pinhead, pithead, pothead, pushead, raghead, rawhead, redhead, replead, retread, roadbed, saphead, see red, sigfred, sofabed, subhead, sudafed, sunsted, tancred, testbed, threadx, towhead, umstead, warhead, webhead, westfed, winsted, wowhead

8 letters:
acidhead, armested, armstead, ass-head, axe head, baby bed, baldhead, bankhead, banstead, barehead, barrhead, beakhead, bedstead, beebread, bespread, big-head, billhead, bitthead, bluehead, bolthead, bonehead, boofhead, bow-head, braehead, bridebed, brodhead, buckhead, bulkhead, bullhead, bumstead, bunk bed, burghead, butthead, calibred, campaned, camp bed, childbed, clubhead, cockhead, cokehead, craghead, dark red, deadhead, deathbed, deckhead, deep red, despread, dispread, dopehead, dotehead, drawhead, dropdead, drophead, drumhead, dullhead, dumbhead, englbred, firstfed, flathead, foodshed, foreread, foresaid, forkhead, fortread, frybread, fuckhead, gainsaid, gearhead, gilthead, glycomed, go-ahead, goathead, go ahead, hardhead, hellbred, high-red, highbred, hogshead, holstead, holyhead, homebred, hot-head, ill-bred, infrared, interbed, jolthead, knobhead, lakehead, lake bed, lie-abed, linebred, lip-read, lochhead, longhead, lunkhead, masthead, meathead, milstead, minehead, misdread, moorhead, muirhead, nailhead, newlywed, newstead, node-red, olmstead, overbred, overhead, pierhead, pig lead, pink-red, pissabed, playdead, playhead, plowhead, pot-head, purebred, pyspread, railhead, re-tread, red lead, ringhead, riverbed, rose-red, rosehead, rose bed, ruby-red, runghead, rust-red, sheetfed, skinhead, slaphead, slugabed, snaphead, sofa bed, softhead, sorehead, sowbread, spithead, spoonfed, staghead, stephead, test bed, toadhead, toolhead, tow-head, truebred, twin bed, underfed, unionfed, unpruned, unthread, upthread, volstead, wanstead, waterbed, waybread, wellbred, wellhead, wine-red, winstead, wirehead, woodhead, woodshed, woolhead

9 letters:
abovesaid, acid-head, acid head, addlehead, aforesaid, armistead, arrowhead, bald-head, beachhead, beak-head, beckstead, bedspread, bee-bread, blackhead, blacklead, blockhead, blood-red, bloodshed, braindead, breadhead, breastfed, brick red, broadhead, butt-head, cadenhead, city-bred, clapbread, clip lead, clouddead, club-head, club head, cockshead, congo red, coral-red, cornbread, courtbred, crackhead, craighead, creek bed, crossbred, crosshead, deep-read, dittohead, divan bed, doorstead, drop-dead, drop-head, drop dead, earthbred, evil dead, farmstead, flatbread, flinthead, floodhead, flowerbed, fry bread, gateshead, get ahead, godlyhead, goodbread, go to bed, greenhead, grinstead, grouthead, half-bred, half-dead, half-read, hampstead, hard lead, hash head, head lice, high-bred, hollyhead, home-bred, homestead, hornyhead, horsehead, infra-red, jollyhead, juicehead, krauthead, link-dead, live/dead, lookahead, loosehead, lowlihead, lustihead, merestead, metalhead, mistihead, moorehead, moosehead, motorhead, must-read, nail-head, negrohead, neverdead, noonstead, nut bread, outspread, overtread, peterhead, pill head, plumstead, poppyhead, powerhead, printhead, pure-bred, radiohead, riverhead, rivethead, roadstead, roughhead, roundhead, rye bread, scarehead, screwhead, seemlyhed, set ahead, sheephead, shewbread, shinehead, shorthead, showbread, sick-abed, skullhead, skunkhead, smackhead, snakehead, soothsaid, sourbread, sourcefed, spearhead, stairhead, stakehead, star-read, steelhead, stop dead, stourhead, suedehead, swellhead, thickhead, towelhead, trailhead, truck bed, true-bred, tulip bed, twin-lead, underbred, underhead, waterhead, watershed, water bed, waynehead, well-bred, well-read, whitbread, whitehead, wronghead, zebrahead

10 letters:
addle-head, arrow-head, baby's bed, backspread, barrelhead, beetlehead, bellowhead, billethead, birkenhead, black-lead, black lead, blodeuwedd, bobblehead, bonnethead, bottlehead, brain-dead, brain dead, bridgehead, bright-red, bronze-red, bubblehead, buckethead, bufferhead, bufflehead, bullethead, chaos;head, cheesehead, cherry-red, cherry red, chrome red, copperhead, cow's head, crispbread, cynghanedd, dark bread, date bread, double bed, dragonhead, drearihead, drowsihead, dunderhead, eraserhead, featherbed, fiddlehead, figurehead, filter bed, giddy-head, goldthread, hammerhead, harddihead, horse-head, horsebread, human head, humblehead, indian red, jerkinhead, jolterhead, knighthead, laverbread, letterhead, loggerhead, maidenhead, marblehead, medusahead, mothershed, muddlehead, murphy bed, muttonhead, niggerhead, noodlehead, orange-red, orange red, overspread, oysterhead, oyster bed, packthread, petrolhead, pirouetted, plow ahead, poppy-head, portishead, purple-red, rattlehead, rotor head, rudderhead, saddlebred, seeing red, sheepshead, shock-head, shortbread, shovelhead, showerhead, sight-read, silverhead, single bed, sleepyhead, sleigh bed, snake-head, spectramed, speed-read, spreadhead, springhead, stone-dead, sweetbread, swinebread, timberhead, tough-head, turkey red, turnip bed, turtlehead, type-ahead, whitebread, white lead, widespread, wingspread, woodenhead, yellowhead, zipperhead

11 letters:
beastlihead, beetle-head, black bread, blunderhead, boroughhead, break bread, broadspread, brown bread, chinese-red, chowderhead, chucklehead, drunkenhead, featherhead, feather bed, flower head, gingerbread, girdlestead, hilton-head, hilton head, hollinshead, in the head, in the lead, judge dredd, jumper lead, knucklehead, leatherhead, left 4 dead, light bread, marketstead, mothershead, multithread, onion bread, pencil lead, pilot bread, pointy-head, pudden-head, quick bread, repair shed, speech-read, spoon bread, springstead, thickspread, thunderhead, travelstead, trundlehead, trundle bed, wanlockhead, weatherhead, white-bread, white bread, woolly-head

12 letters:
alveolar bed, anthony head, bacteria bed, banana bread, batter bread, blackish-red, brownish-red, built in bed, chuckle-head, cittern-head, country-bred, crowned head, cuckoo bread, death's head, dumbfoundead, enkerchiefed, far-infrared, feather-head, fountainhead, french bread, garlic bread, get into bed, gluten bread, graham bread, head-to-head, hollingshead, hospital bed, lochgilphead, mahogany-red, marriage bed, monkey-bread, monkey bread, mushroomhead, nominal head, platform bed, pocket bread, pudding-head, pudding head, purplish red, railroad bed, raisin bread, running head, screw thread, singlethread, stagger head, standardbred, swelled head, talking head, thoroughbred, thrust ahead, trippie redd, venetian red

13 letters:
asparagus bed, capillary bed, cheese spread, christiansted, cylinder head, disk overhead, dragon's head, golden thread, italian bread, loaf of bread, magnetic head, metroid dread, near-infrared, propellerhead, shades of red, skillet bread, sounding lead, standard-bred, sugar of lead, the evil dead

14 letters:
armed bullhead, atomic warhead, brown bullhead, chris bumstead, cinnamon bread, cubbridge-head, phantom thread, seminole bread, staggered head, straight-ahead

15 letters:
agnes moorehead, department head, heels over head, nuclear warhead, the living dead

16 letters:
army of the dead, ash vs evil dead, command overhead, common arrowhead, false dragonhead, irish soda bread, jewish rye bread, rhode island red, whole meal bread

17 letters:
caterpillar tread, false dragon head, quilted bedspread, shaun of the dead, swedish rye bread, whole wheat bread, without bloodshed

18 letters:
boston brown bread, caraway seed bread, skillet corn bread

20 letters:
beavis and butt-head

21 letters:
fear the walking dead, thermonuclear warhead

22 letters:
escape from spiderhead, highschool of the dead, those who wish me dead

23 letters:
anotherloverholenyohead, mary elizabeth winstead, vice-admiral of the red

24 letters:
night of the living dead

27 letters:
command processing overhead

29 letters:
the detective is already dead