Or search: gap, film, plug, pose, slip, tuck, dicky, embed, foist, graft, imbed, inset, shoot, infix, append
1 Syllable: S
learned
2 Syllables: SU
Bertrand, Berwick, blurted, burdened, Burnet, circuit, fervid, girded, herded, hermit, perfect, permit, purposed, skirted, stirrup, surfeit, syrup, target, thirsted, turgid, turnip, turret, verdict, whirlwind, worded, worsened, worship, worshipped, worships, worsted
3 Syllables: USU
adverted, alerted, allergic, asserted, averted, concerted, converted, deserted, determined, diverted, exerted, imperfect, interpret, inverted, perverted, reasserted, reverted, subverted
4 Syllables: UUSU
overburdened, predetermined, unconverted, undetermined

Found 53 words across 4 groupings. Skipped 9 excess words of a similar stem.