Or search: unpersuaded, unregenerate, unregenerated
1 Syllable: S
learned
2 Syllables: SU
Berwick, blurted, Burnet, herded, perfect, permit, skirted, thirsted, turgid, verdict, whirlwind, worded, worship, worsted
3 Syllables: USU
adverted, alerted, allergic, concerted, converted, deserted, diverted, exerted, imperfect, inserted, inverted, perverted, reasserted, reverted, subverted
4 Syllables: UUSU
predetermined, undetermined

Found 32 words across 4 groupings. Skipped 3 excess words of a similar stem.