Or search: undoable, unattainable, unachievable
1 Syllable: S
bulb, bulge, bulk, cul, cull, cult, curl, dull, Earl, Earle, Earls, girl, gulf, gull, gulp, hulk, Hull, hurl, lull, Mull, null, pearl, pulp, pulse, skull, sul, swirl, whirl, will, world
2 Syllables: SU
adult, impulse, insult
2 Syllables: US
Biol, consult, convulsed, divulge, engulf, exult, indulge, occult, repulse, result, unfurled
3 Syllables: UUS
agreeable, foreseeable
4 Syllables: UUUS
disagreeable
5 Syllables: SUUUU
recognisable

Found 48 words across 6 groupings. Skipped 30 excess words of a similar stem.