2 letters:
it

3 letters:
bit, fit, hit, kit, nit, pit, sit, tit, wit

4 letters:
brit, chit, emit, fitt, flit, grit, hitt, kitt, knit, litt, mitt, obit, omit, pitt, quit, ritt, skit, slit, smit, spit, vitt, whit, witt, writ

5 letters:
-quit, 8-bit, admit, askit, atlit, a bit, befit, bewit, bitte, blitt, britt, bukit, dalit, delit, demit, ditte, do it, dritt, e-fit, fitte, flitt, fritt, fytte, gitte, hitte, izmit, jitte, judit, jytte, kitte, l-sit, legit, mcfit, nakit, on it, plitt, pritt, quitt, refit, relit, remit, rohit, rs-68, scrit, sitte, smitt, split, squit, stitt, telit, titte, to it, tritt, ttytt, twitt, unfit, unlit, unmit, unwit, whitt, witte

6 letters:
16-bit, 32-bit, acquit, anahit, and it, armpit, attrit, bankit, baryte, buy it, canlit, commit, confit, davitt, devitt, dewitt, dritte, dualit, fitbit, fsplit, gaslit, get it, granit, illite, it-wit, leg it, mcnitt, menhit, misfit, mishit, no-hit, oblite, outfit, outhit, outwit, permit, pig it, plyght, polkit, premit, qiskit, quitte, replit, savitt, schmit, shmidt, splitt, ssh-68, submit, sunlit, teufit, tidbit, titbit, twilit, unknit, webkit, weskit, xsplit

7 letters:
amazfit, appetit, aquavit, backfit, backlit, barritt, bar bit, bed-sit, boblitt, burditt, cockpit, conflit, cool it, cosewic, datakit, dewitte, dikshit, dogshit, douthit, duravit, firelit, fit-fit, forewit, frogbit, gag-bit, gillett, hawkbit, heremit, homekit, hoof it, lafitte, lose it, luck it, make it, manumit, mashhit, megahit, moonlit, overhit, parasit, pelesit, petzite, politte, pro-fit, quadbit, readmit, resplit, rootkit, schlitt, schmidt, schmitt, schnitt, schritt, sirikit, spotlit, tar pit, the pit, toolkit, tu-whit, two-bit, ufc 268, unaquit, unsplit

8 letters:
about it, baby-sit, base hit, beckwitt, berashit, bereshit, bereshyt, blue tit, bore bit, bush tit, carmelit, chalkpit, clampitt, core bit, crossfit, curb bit, dendrite, douthitt, drillbit, flush it, framekit, frog-bit, frostbit, greenlit, half-wit, hard-hit, heathkit, heraklit, hissyfit, hypocrit, interdit, intermit, intromit, isn't it, keep-fit, king-hit, laffitte, mandalit, mess kit, netsplit, parasyte, pettitte, photofit, pilibhit, presplit, proudfit, recommit, resubmit, retrofit, rj mitte, rock bit, snakebit, snuff it, superbit, superhit, tool kit, transmit, underwit, under it, videofit

9 letters:
after-wit, an/apg-68, arrowslit, artoolkit, b-toolkit, beraishit, blade bit, bleachbit, candlelit, centerbit, cross bit, drill bit, euosmitte, every bit, frogs-bit, gill slit, grassquit, hand-knit, hipocrite, holy writ, horgavitt, house-sit, hypocrite, identikit, indicavit, interknit, loschmidt, majapahit, match-fit, miryachit, myriachit, palafitte, parikshit, pilot bit, pinch-hit, pissenlit, pretermit, quamoclit, see to it, spade bit, stone pit, tanartkit, tightknit, twist bit, underwrit, wagon-lit, well-knit, whole kit

10 letters:
ask for it, bananaquit, be with it, bit-by-bit, bit by bit, cable-knit, canker-bit, cannon-bit, center bit, centre bit, chkrootkit, close-knit, gin and it, hippocrite, hunger-bit, is this it, mother wit, packagekit, parity bit, retransmit, roller bit, sewing kit, sheepsplit, size of it, switch-hit, take a hit, tight-knit, toilet kit, travel kit, wait-a-bit, weatherbit, worldremit

11 letters:
banana quit, counterfeit, cuckoo-spit, diddly-shit, double-knit, double knit, goldschmidt, harzburgite, querschnitt, stock split, throw a fit, tia/eia-568, waldschmidt, weather-bit, work permit, you said it

12 letters:
ansi/tia-568, banana split, closely-knit, closely knit, douglas pitt, drilling bit, kleinschmidt, liberty chit, loosely knit, significavit, tightly knit

13 letters:
alica schmidt, baseball mitt, brace and bit, circular-knit, dylan schmidt, expansion bit, expansive bit, hamburg-mitte, hammerschmidt, hawk and spit, judicial writ, kuhlenschmidt, lickety-split, lickety split, messerschmidt, messerschmitt, orchestra pit, reverse split, the least bit, waffenschmidt, wolfenschmidt

14 letters:
chicago outfit

15 letters:
allison schmitt, building permit, carpenter's kit, have a go at it, just go with it, the thick of it

16 letters:
maisons-laffitte

17 letters:
on the face of it, sino-soviet split, timothy b. schmit

19 letters:
reverse stock split

21 letters:
as luck would have it

25 letters:
unbreakable kimmy schmidt