2 letters:
lb

5 letters:
bound, found, hound, mound, pound, round, sound, wound

6 letters:
'round, -bound, abound, around, csound, downed, gowned, ground, qsound, stound, swound, towned

7 letters:
aground, astound, browned, clowned, cofound, crowned, drowned, enround, enwound, expound, facound, frowned, gepound, imbound, impound, inbound, infound, mahound, rebound, redound, refound, resound, rewound, unbound, unfound, unowned, unround, unsound, unwound, upbound, yground

8 letters:
allround, axewound, compound, confound, consound, dashound, disbound, dumfound, elkhound, fogbound, foxhound, go-round, gunbound, icebound, lymhound, missound, newfound, outbound, outsound, potbound, prebound, profound, propound, re-sound, renowned, runround, seabound, sj-sound, surround, ungowned, unground

9 letters:
air-bound, all-round, ask round, barkbound, bearhound, bedground, boarhound, browbound, buckhound, casapound, casebound, chowhound, coonhound, cpu-bound, deerhound, deskbound, dog pound, downbound, draghound, egg-bound, embrowned, eurohound, freesound, gazehound, getaround, go-around, go around, grayhound, greyhound, hardbound, harehound, hellbound, hellhound, hidebound, hoarhound, homebound, hoofbound, horehound, howlround, ironbound, limehound, lobspound, misground, new-found, newground, newshound, newsround, outground, overwound, pot-bound, raw wound, rockbound, rockhound, rootbound, runaround, semiround, skinbound, slowhound, snowbound, softbound, staghound, starbound, top round, turnround, uncrowned, westbound, windbound, wolfhound, wrapround

10 letters:
aftersound, all-around, background, bed-ground, bellybound, bloodbound, bob around, boozehound, brassbound, bum around, campground, chairbound, clothbound, come round, crop-bound, dachshound, decompound, desk-bound, discrowned, duty-bound, earthbound, fairground, fantasound, foot-pound, foreground, get around, gold-bound, half-bound, half-round, home-bound, housebound, inch-pound, infrasound, interwound, irrenowned, lie around, misexpound, moon-round, nursehound, otterhound, overabound, overground, paperbound, playaround, playground, pull round, rock-bound, rug-gowned, run-around, run around, scalebound, showground, sighthound, siteground, slothhound, sluthhound, snow-bound, soundhound, southbound, spellbound, stormbound, surrebound, troy pound, turnaround, ultrasound, unconfound, well-bound, well-found, whip-round, wood-bound, workaround, wraparound, year-round

11 letters:
aboveground, belowground, boss around, brass-bound, bring round, bump around, cast around, cloth-bound, come around, daily round, directsound, earth-bound, fool around, frost-bound, gain ground, grave mound, hang around, holy ground, honor-bound, irish pound, jazz around, kick around, loll around, look around, lower bound, mess around, mill around, moon around, mope around, move around, muck around, musclebound, otter hound, pass around, play around, plott hound, puget sound, push around, roll around, run aground, send around, sensurround, shootaround, shunt-wound, sleuthhound, smoothhound, spell-bound, spin around, stoneground, strikebound, superabound, tool around, turn around, underground, upper bound, vowel sound, walk around, water-bound, work-around, wrap-around, year-around

12 letters:
above-ground, afghan hound, basset hound, battleground, bottom round, bring around, burial mound, circle round, clown around, drive around, electrosound, honour-bound, horse around, merrygoround, muscle-bound, office-found, pine-crowned, series-wound, sleuth-hound, slosh around, slush around, smooth-hound, solid ground, speech sound, spiral-bound, stick around, stone-ground, swing around, syrian pound, twist around, voiced sound, walker hound, waltz around, weatherbound, wheel around, whirl around

13 letters:
air-to-ground, british pound, burial ground, circle around, common ground, cypriot pound, figure-ground, freshlyground, gazelle hound, leather-bound, lounge around, middle-ground, monkey around, outward-bound, parade ground, picnic ground, potter around, putter around, quarter-bound, sausage hound, splash around, teeing ground, weather-bound, winter-ground

14 letters:
burying ground, camping ground, cannibal mound, egyptian pound, georgenotfound, homeward-bound, hunting ground, lebanese pound, lost-and-found, merry-go-round, plot of ground, proving ground, revolve around, safe and sound, sound-on-sound, sudanese pound, triple-crowned, world-renowned

15 letters:
black horehound, breeding ground, fetid horehound, piece of ground, pleasure-ground, pleasure ground, sleeping around, stamping ground, steeple-crowned, supradecompound, walker foxhound, water horehound, white horehound

16 letters:
anchorage ground, common horehound, english foxhound

17 letters:
american foxhound, italian greyhound, long island sound, screen background

18 letters:
get off the ground, hole in the ground, stinking horehound

19 letters:
decemberunderground

20 letters:
gill-over-the-ground, theater-in-the-round, theater in the round, theatre-in-the-round, the other way around

21 letters:
theaters-in-the-round, the fox and the hound