Or search: goal, lens, grail, lense, target, grammar, neutral, clinical, concrete, existent, accusative, impersonal, verifiable, nonsubjective
2 Syllables: SU
checklist, fetish, reddish, sexes, wreckage
3 Syllables: SUU
effective
3 Syllables: USU
affective, Alexis, collective, connective, corrective, deceptive, defective, detective, directions, directive, elective, invective, objectives, perceptive, perspective, prospective, protective, receptive, reflective, respective, selective, subjective
4 Syllables: UUSU
ineffective, introspective, irrespective, retrospective

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