1 syllable:
'em, 'm, -some, bd-rom, bluhm, brum, brumm, bum, chum, clum, come, comme, crum, crumb, crumm, cum, ddrum, druim, drum, drumm, dslam, dum, dumb, dumm, dzbb-am, dzrj-am, from, frum, gd-rom, glum, gmbh, grum, gthumb, gum, gumm, hm, hmm, hrtem, hum, humm, khnum, klumb, krum, krumm, krumme, kumm, lum, lumb, lumm, lumme, maam, mum, mumm, mumme, nccam, ngcam, numb, pflum, phlem, phleme, plum, plumb, rhomb, rum, schem, schrum, schtum, schum, schumm, scrum, scum, scumm, shrum, shtum, shum, skrim, slum, smram, some, strum, stum, stumm, stumme, sum, summe, swum, them, thrum, thum, thumm, tshombe, um, umm, v-comb, vl-srsam, xrsam, yum

2 syllables:
aksum, alum, ancrum, baucum, become, benumb, bethumb, bithumb, boyum, branscome, breadcrumb, cancrum, carum, checksum, columb, deblum, dishyum, djarum, encom, exum, faiyum, first-come, freedumb, goodrum, guthrum, herefrom, hohum, hop-thumb, humdrum, ikwum, income, larum, lump-sum, marum, mccrum, mccrumb, narum, neu-ulm, noucome, outcome, pileum, plethrum, sharum, steak-umm, stepmom, succumb, tear-thumb, tecum, therefrom, unplumb, wellcome, wherefrom, yab-yum, yum-yum, yumyum

3 syllables:
adnexum, amarum, amphicome, barathrum, beetlebum, bungarum, deaf-and-dumb, disbecome, labarum, misbecome, mishawum, no-see-um, norodom, obesum, overcome, physarum, podarthrum, pyrethrum, rule-of-thumb, saccharum, sisarum, tartarum, unbecome, unbenumb, zero-sum

4 syllables:
abomasum, arisarum, erucifrom, falciparum, glyoxysome, granulosum, hedysarum, hop-o'-my-thumb, pigmentosum, stenotaphrum

5 syllables:
tetrapharmacum

6 syllables:
oleosaccharum