2 letters:
ot

3 letters:
cot, dot, got, hot, jot, lat, lot, not, ott, pot, rot, sot, tot, wat

4 letters:
baht, blot, bott, clot, haut, khat, knot, lott, mott, plot, pott, scot, shot, slot, snot, spot, swat, taut, trot, watt

5 letters:
allot, ascot, aught, a lot, begot, besot, butat, croat, herat, kiaat, lotte, minot, motte, ought, robot, sadat, scott, squat, yacht, zakat

6 letters:
ablaut, abwatt, ararat, avocat, bespot, bharat, bought, cannot, caught, forgot, fought, haught, hotpot, inkpot, jampot, kurrat, loquat, mascot, naught, nought, ocelot, schott, sexpot, sought, taught, teapot, umlaut, unknot, upshot

7 letters:
apricot, bibelot, bowknot, boycott, brought, calotte, camelot, cocotte, culotte, cypriot, dashpot, dogtrot, dry rot, earshot, eyeshot, eyespot, feedlot, flyswat, fraught, fusspot, galipot, garotte, gunshot, haricot, hotshot, hotspot, inkblot, jackpot, job lot, lamotte, may not, potshot, red-hot, sandlot, sunspot, talipot, thought, topknot, tosspot, whatnot, wrought, wyandot

8 letters:
advocaat, aeronaut, aquanaut, argonaut, bell cot, besought, big shot, buckshot, bullshot, cachalot, cachepot, crackpot, culottes, dash-pot, entrepot, eschalot, fleshpot, foot rot, fox-trot, gallipot, gigawatt, have got, headshot, honeypot, hotchpot, huguenot, jog trot, kilowatt, lancelot, longshot, megawatt, microdot, misbegot, mug shot, must not, oceanaut, one-shot, one shot, overshot, paraquat, ring rot, root rot, set shot, six-spot, slapshot, slipknot, snapshot, soft rot, stinkpot, stockpot, ten-spot, unsought, untaught

9 letters:
astronaut, bank shot, bethought, bird shot, black rot, bloodshot, brown rot, case shot, chip shot, chop shot, coffeepot, coin slot, concordat, cosmonaut, drop shot, duck shot, dunk shot, five-spot, flat knot, flowerpot, foul shot, four-spot, golf shot, grapeshot, halo spot, high spot, hook shot, inwrought, jump shot, liver rot, long shot, loop knot, love knot, mail slot, methought, milliwatt, moon shot, nightspot, nine-spot, onslaught, pine knot, polka dot, reef knot, sheep rot, slingshot, soft spot, time slot, unthought, weak spot, whole lot, wyandotte

10 letters:
baking hot, black knot, blind spot, blood clot, blood knot, bottom rot, chamberpot, chimneypot, crack shot, distraught, eight-spot, globe-trot, juggernaut, jungle rot, liver spot, masse shot, montserrat, nouakchott, on the dot, overbought, pepper pot, pitch shot, pivot shot, rifle shot, round shot, scoop shot, seven-spot, silverspot, sword knot, vacant lot

11 letters:
barrel knot, beauty spot, countershot, dreadnaught, dreadnought, forethought, french knot, granny knot, hard-fought, indian shot, lobster pot, melting pot, on-the-spot, overwrought, parking lot, plague spot, rising trot, scattershot, self-taught, square knot, tennis shot, turkey trot, yellow spot

12 letters:
aforethought, afterthought, aleph-nought, booster shot, charity shot, cleanup spot, diddly-squat, free thought, gordian knot, lover's knot, merrythought, passing shot, racing yacht, sans-culotte, scot and lot, sir lancelot, sitting trot, stopper knot, store-bought, watering pot, windsor knot

13 letters:
approach shot, backhand shot, black apricot, canister shot, dried apricot, forehand shot, truelove knot, vacation spot, weaver's knot

14 letters:
common apricot, expansion slot, purple apricot, refractory pot, second thought, sultan of swat, surgeon's knot

15 letters:
basketball shot, deep in thought, good-for-naught, line of thought, powder and shot

16 letters:
abstract thought, fisherman's knot, food for thought, japanese apricot, train of thought

17 letters:
school of thought, true lover's knot

18 letters:
freedom of thought

19 letters:
matthew walker knot, more often than not

23 letters:
philadelphia pepper pot