3 letters:
ass, cas, das, gas, ras, sas

4 letters:
alas, bass, bras, cass, dass, fahs, fass, gass, glas, hass, jass, kass, klas, kras, lass, mass, nass, pass, plas, sass, tass, vass, yass

5 letters:
alass, amass, amcas, basse, blass, brass, casse, chass, class, crass, dcass, ddass, drass, ecass, emass, fasse, frass, gasse, grass, ipass, kasse, klass, krass, kvass, lasse, mass., masse, miass, nasse, ofgas, plass, prass, rasse, recas, sasse, shass, tasse, trass, umass, velas, wrass, xmass, yeahs

6 letters:
admass, airgas, alsace, anlass, audace, badass, besace, brasse, bypass, camass, chagas, chasse, classe, crasse, dclass, depass, fatass, glasse, grasse, harass, i-pass, klasse, morass, navras, plasse, potass, repass, strass, trasse, vorace, wrasse

7 letters:
a-class, airmass, bad-ass, big-ass, bindass, bumpass, by-pass, damasse, declass, donbass, e-glass, e-zpass, eagrass, energas, fat-ass, filasse, finglas, forpass, hardass, impasse, ipocras, jackass, keepass, kickass, kompass, kuzbass, lardass, lowpass, metglas, molasse, outpass, portass, sambass, seabass, serfass, she-ass, strasse, sunpass, surpass, vanasse, verglas, wiseass, yankass, ypocras

8 letters:
aairpass, amerigas, autopass, bandpass, bare-ass, bierglas, bio-mass, botopass, burgrass, crevasse, cutgrass, declasse, dumb-ass, eelgrass, efficace, europass, eyeglass, half-ass, hard-ass, hardbass, kick-ass, kiss-ass, landmass, lard-ass, lastpass, madecass, midgrass, newgrass, nordpass, nutgrass, outclass, outlasts, overpass, owlglass, piepgras, ribgrass, ryegrass, sawgrass, seagrass, smartass, spyglass, sub-bass, subclass, sunglass, timepass, trespass, wise-ass

9 letters:
ahnenpass, band-pass, beargrass, bentgrass, bluegrass, candlemas, candy-ass, classpass, contrasts, cordgrass, crabgrass, cut-glass, cut-grass, deergrass, egg-glass, fiberglas, forecasts, hippocras, hourglass, isinglass, itar-tass, jenny-ass, knotgrass, lambastes, lovegrass, low-class, martinmas, metaclass, middlemas, motorbass, moviepass, overclass, plexiglas, ricegrass, rushgrass, rye-grass, sandglass, sassafras, sea-grass, silkgrass, smart-ass, snodgrass, tallgrass, tarantass, tight-ass, top-class, transpass, tresspass, underpass, wineglass, wiregrass, worldpass, yardgrass

10 letters:
aftergrass, arrowgrass, bell-glass, bent-grass, bromegrass, bunchgrass, candlemass, cane-grass, cheatgrass, couchgrass, curtelasse, demi-tasse, fiberglass, fibreglass, fieldglass, galloglass, goosegrass, groundmass, high-class, hour-glass, interclass, lemongrass, perspicace, plexiglass, quackgrass, quatermass, ravenglass, rush-grass, sassafrass, shortgrass, sparagrass, speargrass, stormglass, superclass, supergrass, tall-grass, underclass, untertasse, upperclass, watchglass, wheatgrass, witchgrass, worldclass

11 letters:
after-grass, bottlegrass, couch-grass, dallisgrass, double-bass, first-class, gallowglass, goose-grass, hoofdklasse, hoppergrass, lower-class, masterclass, meadowgrass, middleclass, peppergrass, plate-glass, psycho-pass, rankin/bass, shangri-las, short-grass, sonderclass, switchgrass, third-class, upper-class, watch-glass, weierstrass, wheat-grass, world-class

12 letters:
africa/brass, boardingpass, bottle-grass, bristlegrass, canary-grass, cotton-grass, ecclesiastes, economyclass, fourth-class, gangstagrass, hardinggrass, johnsongrass, meadow-grass, middle-class, montparnasse, push-to-pass, ripple-grass, scurvy-grass, second-class, sparrowgrass, weatherglass

13 letters:
burning-glass, looking-glass, stained-glass, thorough-bass, timothy-grass, working-class

14 letters:
scorpion-grass

17 letters:
upper-lower-class

18 letters:
lower-middle-class, upper-middle-class

4 letters:
hats, katz, bats, cats, fats, rats

5 letters:
spats, flats, pat's

6 letters:
that's