2 letters:
ad

3 letters:
add, bad, cad, dad, fad, gad, had, lad, mad, nad, pad, rad, sad, tad

4 letters:
brad, chad, clad, dyad, ecad, flad, gadd, glad, grad, hadd, hlad, ipad, khad, ladd, madd, scad, shad, tadd, thad, vlad

5 letters:
accad, aicad, ariad, arvad, audad, ayyad, bedad, begad, cadde, chadd, codad, copad, cycad, d-pad, decad, dryad, ectad, entad, gladd, gradd, harad, hexad, igadd, imdad, i had, johad, kicad, ladde, mirad, ncadd, nicad, nomad, octad, p-cad, plaid, quad-, radde, retad, riyad, sadad, schad, shadd, sprad, stadd, strad, tradd, triad, tvpad, unsad, vorad, yclad, ydrad, zedad, zycad

6 letters:
alclad, alidad, anabad, aoudad, behadd, chabad, ciudad, cuidad, do-dad, doodad, dradde, ekblad, ershad, farhad, fatlad, fnulad, forbad, go bad, heptad, holcad, inkpad, joypad, keypad, maldad, manpad, mashad, mirsad, mossad, narsad, nawcad, ni-cad, nomade, pentad, piedad, pindad, reclad, retrad, riyadh, shabad, shadde, sinbad, tempad, tetrad, unclad, unctad, unidad, unilad, verdad

7 letters:
almodad, almohad, amistad, amstrad, and had, aqualad, ar-ra'd, arm pad, autocad, autorad, blutbad, brl-cad, calidad, caridad, cathbad, comrade, cookpad, coolpad, crawdad, dextrad, dhanbad, dhrupad, eckblad, footpad, freecad, frontad, galahad, gamepad, geekdad, grabcad, grandad, helipad, henadad, hip pad, hot pad, humedad, huzzaed, ideapad, isograd, kneepad, kvistad, leafpad, leappad, lenkrad, manapad, mathcad, miandad, notepad, not bad, octodad, razgrad, rug pad, shinpad, sindbad, skidpad, skyclad, soledad, spradde, stepdad, thappad, too bad, triclad, vanidad, want ad, wattpad, wildbad, wordpad, zwembad

8 letters:
all-clad, angharad, armstrad, blacksad, body pad, branstad, bricscad, cephalad, compuadd, dampfbad, densidad, dignidad, etherpad, facultad, feel-bad, granddad, halmstad, igualdad, ironclad, iron lad, josh gad, kjenstad, knee pad, libertad, librecad, like mad, lily pad, magistad, mailclad, maligrad, medelpad, mongstad, novogrod, olympiad, openscad, overglad, polyclad, postgrad, randstad, rapidcad, realidad, semiclad, shahrzad, sinhagad, soap pad, sociedad, superadd, superdad, they had, thinkpad, touchpad, trackpad, transcad, trinidad, tsargrad, variedad, vendidad, visegrad, voluntad, zindabad

9 letters:
ahmadabad, ahmedabad, ashkhabad, autoridad, capacidad, comodidad, comunidad, drvengrad, elbow pad, eternidad, facilidad, faridabad, fidelidad, full-clad, gamzigrad, habilidad, hamadryad, heathclad, hermandad, humanidad, hyderabad, innistrad, intimidad, jotterpad, kalapahad, khongirad, khuldabad, lake chad, latinidad, launchpad, leningrad, mail-clad, marienbad, moradabad, mouse pad, naukograd, olympiade, olympiads, oscuridad, petrograd, pine-clad, pratapgad, schildpad, seguridad, sinistrad, sketchpad, snow-clad, springpad, stamp pad, theodahad, thigh pad, tinkercad, undergrad, velingrad, velocidad, vine-clad, volgograd, wrist pad

10 letters:
adversidad, allis shad, armor-clad, bosilegrad, carpet pad, dark triad, diane ladd, dificultad, featherpad, hasselblad, hispanidad, integridad, intensidad, kettenkrad, kirovograd, kirovohrad, launch pad, messagepad, phylloclad, raving mad, river shad, round scad, scratchpad, shamshabad, sketch pad, stalingrad, steel-clad, svilengrad, tongue-pad

11 letters:
armour-clad, blagoevgrad, farrukhabad, fraternidad, heating pad, kaliningrad, message pad, murshidabad, posibilidad, profundidad, scratch pad, sir galahad, solidaridad, stalinogrod, universidad, writing pad

12 letters:
breaking bad, cleaning pad, deadbeat dad, dimitrovgrad, electricidad, elisavetgrad, mattress pad, newspaper ad, personalidad, probabilidad, sajid-farhad, scouring pad, secunderabad, shoulder pad, tomislavgrad

13 letters:
fetch-and-add, humancentipad, launching pad, mackerel scad, mackerel shad, real sociedad, scantily clad, yelisavetgrad, yelizavetgrad

14 letters:
voroshilovgrad

15 letters:
capital of chad, responsabilidad

17 letters:
rich dad poor dad

18 letters:
siege of leningrad

20 letters:
battle of stalingrad, common american shad

22 letters:
pfc ludogorets razgrad