Or search: boring, irksome, tedious, tiresome, wearisome, debasement, impairment, degradation, constipation, uninteresting, stultification
2 Syllables: SU
bedding, begging, betting, checking, deafening, dreading, ebbing, Edwin, fretting, getting, heading, letting, leveling, meddling, netting, pecking, reading, reckoning, setting, settling, shedding, spreading, stepping, sweating, threading, threatening, treading, vexing, wedding, wetting, wrecking, wrestling
3 Syllables: SUU
beckoning, bettering, editing, effecting, entering, Evelyn, festering, lessening, lettering, levelling, measuring, menacing, reddening, revelling, severing, threatenings, trespassing, weathering
3 Syllables: USU
abetting, accepting, affecting, annexing, begetting, besetting, collecting, connecting, correcting, detecting, directing, direction, dissecting, electing, endeavoring, erecting, excepting, expecting, forgetting, infecting, injecting, inspecting, neglecting, objecting, perfecting, perplexing, projecting, prospecting, protecting, reflecting, regretting, rejecting, respecting, selecting, subjecting, suspecting, unsettling, upsetting
4 Syllables: USUU
developing, discrediting, embarrassing, endeavouring, enveloping, inheriting
4 Syllables: UUSU
intercepting, intersecting, recollecting, unsuspecting

Found 98 words across 5 groupings. Skipped 4 excess words of a similar stem.