3 letters:
ack, akc, bak, cac, caq, dac, dak, fac, haq, jac, lac, lak, mac, mak, pac, rak, sac, sak, tac, tak, yak, zak

4 letters:
adak, back, brac, dack, flak, hack, jack, kwak, lack, mack, nack, pack, ptak, rack, sack, shaq, spak, stac, tack, trac, trak, wack, yack, zach, zack

5 letters:
.hack, 6lack, aback, aflac, aipac, alsac, anfac, anzac, apsac, attac, backe, bakke, binac, bipac, blacc, black, brack, capac, caque, cdiac, cepac, chack, clack, crack, dirac, dmacc, drack, dsmac, dulac, dysac, eclac, ellac, eniac, fitak, flack, frack, gopac, gopak, h-gac, hacke, haque, harac, hipac, ianac, idrac, ileac, immac, impac, iniac, iupac, jacke, jaque, ka'ak, kacke, kakke, kecak, knack, kodak, kojak, krack, kyack, lakke, laque, lilac, macke, mafac, malac, mblaq, medac, midac, msiac, musac, nacke, nadac, ncpac, njpac, nlnac, nopac, nyack, oblak, ocpac, ontak, padak, pakke, paque, pbkac, plack, pofac, quack, radak, rojak, rtfaq, sadak, sedac, sepaq, shack, sifac, slack, smack, snacc, snack, spack, stack, strac, strak, supac, tabac, tabak, tacke, taque, thack, thrak, tplac, triac, tslaq, tuqaq, undac, wacke, wesak, wewak, whack, wrack, x-pac

6 letters:
abaque, amtrac, anorak, ataque, attack, balzac, bipack, blaque, boback, brakke, braque, calpac, chaque, chirac, chyack, claque, cognac, compaq, craque, deepak, deltak, easiac, ebufac, firaaq, flaque, formac, gempak, h-back, hibaaq, hijack, hoback, ipecac, itaque, jampac, jetpac, kalpac, kodiak, kracke, lacche, lapack, larzac, lojack, macpac, maniac, mauzac, midpac, mikmaq, mirfac, moniac, mosiac, mustac, n-back, navfac, oopack, pebcac, pebcak, pebmac, persac, phrack, placke, plaque, plbkac, prozac, quaque, radiac, ramdac, rempac, repack, ricrac, rimpac, roback, ruback, ryback, sacque, schach, schack, senlac, simpac, socpac, sprack, sremac, strack, t-back, tarmac, termac, thrack, tictac, tritac, unpack, untack, uzmack, wakwak, wejack, wespac, zodiac, zodiak

7 letters:
-maniac, algonac, almanac, amtrack, arnaque, assjack, attaque, aurolac, austrac, autofac, beaulac, bidlack, biopack, bosniac, buyback, cadilac, calpack, cardiac, carjack, champac, chi-raq, cincpac, cinepak, cluniac, colemak, cutback, cuttack, daypack, dieback, dynafac, dynapac, eastpac, eastpak, elegiac, estrack, fatback, feeback, finback, fintrac, flatpak, flyback, fosback, gaillac, grzelak, gum-lac, gun-nac, hanback, hatrack, haystak, hi-jack, hogback, hopsack, httrack, icepack, innopac, interac, jacques, jetpack, layback, linpack, mahopac, malinak, manjack, masback, matlack, medivac, mi'kmaq, mitilac, mostack, mudpack, muntjak, netback, nethack, niblack, oplenac, outback, payback, peapack, pinback, placque, pontiac, prepack, qaanaaq, rakshak, ransack, ratpack, redback, redhack, rowback, runback, sangiac, schlack, schnack, schrack, schupak, sea-tac, setback, shediac, shellac, shishak, shoepac, similac, simulac, sixpack, skyjack, sowback, spiewak, stracke, sunback, takk..., tic-tac, tieback, tintack, towsack, tupilaq, unstack, wanaque, wavpack, wayback, webpack, westpac, winback

8 letters:
acardiac, afrojack, al-boraq, all-trac, almanach, almanack, ammoniac, amnesiac, aphasiac, armoniac, auerback, autorack, backpack, backrack, ballsack, bar-back, bareback, blowback, blu-tack, blueback, bluejack, bootjack, brainiac, brumback, buy-back, cadillac, callback, cashback, clawback, coatrack, comeback, creashak, demoniac, die-back, dowagiac, drawback, drekavac, dropback, etodolac, eyeblack, failback, fallback, fastback, fastrack, feedback, fireback, fishback, flapjack, flatback, flatpack, flowback, foldback, forblack, forslack, freejack, fullback, gimcrack, giveback, godsmack, govtrack, grayback, greyback, grimjack, gripsack, halfback, hardback, haystack, helitack, highjack, holdback, hornback, humpback, indo-pak, jam-pack, jamstack, jimcrack, kammback, kickback, killpack, knapsack, knitback, laidback, lazyback, lifehack, liftback, lineback, loopback, lootpack, macisaac, mossback, muharraq, murtabak, nonblack, offtrack, ophcrack, overpack, packsack, pauraque, pelusiac, petrofac, pickback, pickpack, pillpack, pingback, playback, plowback, poltrack, pullback, pumpjack, pushback, racetrac, rakeback, ringback, rollback, roorback, rucksack, scatback, seatback, seed-lac, set-back, sexyback, shellack, shoepack, shopback, similack, simoniac, six-pack, skewback, skimback, skipjack, slapjack, slayback, slotback, slowback, snapback, snapsack, snowpack, softback, stanback, substack, sulindac, supermac, swayback, tailback, talkback, thakshak, ticktack, transpac, trictrac, turnback, vanvlack, whipjack, wingback, wolenzac, wolf-pac, wolfpack, woolpack, wurdulac, yolk-sac

9 letters:
almanaque, amberjack, antiblack, applejack, audiomack, backtrack, barmbrack, barnbrack, bioattack, blackjack, bombtrack, boneblack, bookstack, bootblack, brownback, brushback, bushwhack, buttcrack, call-back, camelback, cardiaque, carryback, cash-back, cheapjack, checkback, come-back, comeblack, computrac, comsubpac, condillac, cookshack, coronavac, countback, crookback, crossjack, daemoniac, dottyback, fall-back, fasttrack, feed-back, fightback, flareback, flashback, flat-pack, foreslack, formstack, full-back, gernsback, glasspack, greenback, gunnysack, half-back, halftrack, hard-tack, hatchback, hitchrack, hornwrack, horseback, huckaback, hunchback, ink-black, insomniac, jet-black, knockback, kozemchak, kvelertak, laid-back, lampblack, lancejack, leaseback, left-back, magicjack, marforpac, merrimack, minitrack, multipack, nickajack, notchback, off-track, one-track, openstack, page-jack, paperback, paranaque, paranoiac, pickaback, pickapack, piggyback, pinchback, presspack, pull-back, quillback, racerback, racetrack, railsback, railtrack, razorback, reachback, rejuvelac, ridgeback, roundback, scaleback, sheepback, shell-lac, shellback, shoeblack, sidetrack, slingback, smokejack, soft-tack, spineback, stainback, startrack, steinback, stick-lac, stoneback, swartback, sweepback, sweptback, symposiac, tacmahack, talk-back, thornback, throwback, thumbtack, tick-tack, toastrack, toothback, touchback, trackback, trunkback, two-track, uummannaq, whaleback, whiteback, whitenack, wisecrack, wolf-pack

10 letters:
ahorseback, amarkantak, andromaque, answerback, anti-black, apple-jack, black-jack, blue-black, blue-lilac, bounceback, caddyshack, calicoback, canvasback, carry-back, chargeback, cheap-jack, coal-black, colby-jack, cornerback, crackajack, cul-de-sac, deathtrack, doodlesack, doubleback, epicardiac, ergomaniac, exocardiac, fast-track, fiddleback, fragmentak, frontiniac, gray-black, grey-black, hackensack, hackleback, hackmatack, half-track, hollenback, holsomback, holsonback, hydrocrack, inaamulhaq, inky-black, jiffi-snak, knickknack, knock-back, l0phtcrack, logomaniac, louderback, lumberjack, melomaniac, mondotrack, money-back, monomaniac, multitrack, narrowback, narsarsuaq, natterjack, nickelback, noncardiac, pac-attack, paddywhack, perl-byacc, pickleback, pig-a-back, precardiac, pyromaniac, radioshack, rattleback, right-back, rose-lilac, saddleback, shriekback, silverback, singletrac, sling-back, smarttrack, smokestack, soot-black, soundtrack, splashback, strongback, supplejack, swept-back, switchback, tac-au-tac, theomaniac, thumb-tack, timberjack, tricktrack, turtleback, vantablack, waguespack, warty-back, woollyback, write-back, yellowback

11 letters:
anglomaniac, anthomaniac, aphrodesiac, biofeedback, bottle-jack, brown-black, canvas-back, centre-back, click-clack, crackerjack, culs-de-sac, cyberattack, diamondback, dipsomaniac, double-back, endocardiac, featherback, fiddle-back, flankerback, getdataback, googlewhack, halter-sack, heartattack, hollow-back, hypospadiac, imam-ul-haq, knick-knack, ladder-back, leatherback, leatherjack, lobsterback, meglomaniac, messagepack, metromaniac, minute-jack, monbazillac, mythomaniac, nordictrack, pandemoniac, pericardiac, pitch-black, post-attack, prickleback, pryromaniac, quarterback, salammoniac, scratchback, screwattack, sechserpack, shrink-pack, singletrack, slate-black, sooty-black, steeplejack, stickleback, strickjacke, supple-jack, tlaquepaque

12 letters:
abrar-ul-haq, back-to-back, bibliomaniac, bladderwrack, bluish-black, bluish-lilac, bradycardiac, browserstack, chimneystack, comnavairpac, cracker-jack, diamond-back, diplocardiac, intracardiac, megalomaniac, nymphomaniac, off-the-rack, purple-black, purple-lilac, qikiqtarjuaq, radio-opaque, sal-ammoniac, single-track, tachycardiac, tenure-track, tulipomaniac

13 letters:
counterattack, high-low-jack, misbah-ul-haq, neurofeedback

14 letters:
black-on-black, brownish-black, clickety-clack, counter-attack, inzamam-ul-haq

15 letters:
christian-jaque, eleutheromaniac

17 letters:
beynac-et-cazenac