1 syllable:
massed, mast, mast-, nast, naste, -assed, -blast, -plast, asked, ast, bast, blast, blast-, brassed, brast, cast, caste, chast, classed, clast, fasst, fast, gassed, gast, ghast, glassed, glast, grassed, hast, jfast, kast, kaste, last, laste, passed, past, pcast, plast, rast, raste, sassed, snast, strast, thrast, vast, vfast, vlast, wtfast

2 syllables:
locast, lockfast, makefast, march-past, mercast, mimecast, miscast, molecast, nefast, netcast, newscast, nonpast, nowcast, offcast, ooblast, outcast, outcaste, outclassed, outgassed, outlast, agelast, aghast, amassed, amcast, arblast, attaste, at last, back-blast, backblast, backcast, bare-assed, bedfast, beechmast, belfast, biassed, blogcast, bomb blast, breastfast, broadcast, buckfast, bumbast, by-past, bypassed, bypast, chromecast, coldcast, comcast, contrast, cragfast, crevassed, damast, dbfast, declassed, deskfast, dicast, die-cast, diecast, dismast, divast, downcast, dreamcast, dynast, e'last, erast, fail-fast, fantast, fly-cast, fly-past, forcast, forecast, foremast, forepassed, forepast, forncast, g.fast, gamecast, go past, gymnaste, half-assed, half-mast, halfassed, handfast, harassed, hard-assed, headfast, holdfast, hold fast, icast, icecast, lambast, lambaste, leaf cast, light-fast, lightfast, palast, parcast, phantast, podcast, portlast, precast, qualcast, quantcast, recast, remast, repassed, rogfast, roughcast, ryfast, sand-cast, sandblast, sand cast, screencast, shamefast, shoe-last, shoutcast, sitfast, smart-assed, smashcast, smodcast, soothfast, sportscast, standfast, stand fast, starrcast, statcast, steadfast, stedfast, sunfast, surpassed, symplast, tear-gassed, the last, thronecast, tight-assed, tooncast, top-mast, topmast, trade-last, transfast, trespassed, trispast, type-cast, typecast, umbecast, uncast, upcast, vinfast, vodcast, webcast, whirl-blast, windblast, wormcast

3 syllables:
lymphoblast, medifast, meroblast, mesoblast, mesoplast, metaphrast, metaplast, microblast, microvast, miracast, mitoplast, mizenmast, mizzenmast, monoblast, monoplast, mooring mast, multicast, multifaced, myoblast, mythoclast, narrowcast, needle cast, neuroblast, neuromast, neurospast, next-to-last, open-cast, opencast, orgiast, overcast, acid-fast, acroblast, aftercast, alloplast, altacast, antepast, antispast, anycast, apoplast, archiblast, astroblast, at long last, autoplast, bandobast, bioblast, bioplast, brachyblast, cablecast, centroblast, chiliast, chiroplast, chloroplast, chondroblast, chromoblast, chromoplast, cobbler's last, colloblast, coloplast, colorcast, colorfast, colourcast, colourfast, counterblast, countercast, cranioclast, cuban bast, cybercast, cystoplast, cytoblast, cytoplast, dermoblast, duroplast, ectoblast, endoblast, endocast, endoplast, entoblast, epiblast, everlast, fibroblast, first and last, flabbergast, fore-topmast, foretopmast, gigablast, gonoblast, gymnoplast, gypsoplast, hard-and-fast, hazelcast, hemoblast, hesychast, holoblast, homoplast, hydrocast, hypoblast, intercast, jiggermast, jurymast, jury mast, laserblast, leucoblast, leucoplast, leukoblast, leukoplast, lipoblast, lithoclast, overmast, overpassed, overpast, parablast, paraphrast, pendergast, pentaspast, periblast, periplast, phenoplast, phragmoplast, planoblast, plasmablast, plaster cast, pleonast, pleonaste, polyblast, polycast, polyspast, prendergast, protoplast, pyroclast, rebroadcast, rockpalast, royalmast, royal mast, rubriblast, sarcoblast, sarcoplast, silverfast, simulcast, solo blast, spermoblast, spheroplast, spongioblast, spongoblast, sporoblast, statoblast, superfast, telecast, teloblast, thomas nast, thromboblast, tillinghast, tonoplast, triplecast, trophoblast, trophoplast, ultrafast, undercast, unicast, unsteadfast, unsurpassed, very fast, voltaplast, weathercast, wirecast, xenoblast

4 syllables:
megaloblast, melanoblast, myeloblast, nematoblast, odontoblast, odontoclast, odontoplast, orbitoclast, osteoblast, osteoclast, osteoplast, adenoblast, ameloblast, aminoplast, amyloplast, angioblast, apremilast, audiocast, biblioclast, blepharoplast, cementoblast, chirogymnast, disdiaclast, ecclesiast, ecdysiast, elaioplast, elastoplast, elegiast, embryoblast, encomiast, enthusiast, entosthoblast, erythroblast, etioplast, gonimoblast, granuloblast, gymnasiast, haemangioblast, haematoblast, haematoplast, hemangioblast, hematoblast, iconoclast, idioblast, idoloclast, immunoblast, kinetoplast, lecithoblast, pansporoblast, pronormoblast, sideroblast, slartibartfast, spermatoblast, symposiast, weather forecast

5 syllables:
myofibroblast, nesidioblast, adamantoblast, cnidoblast, cytotrophoblast, dead hand of the past, hemocytoblast, leukocytoblast, phagocytoblast, radio broadcast, religious outcast

6 syllables:
kaliningrad oblast

7 syllables:
syncytiotrophoblast