Or search: discriminating
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, objective, perceptive, perspective, prospective, protective, receptive, reflective, respective, subjective
4 Syllables: UUSU
ineffective, introspective, irrespective, retrospective

Found 31 words across 4 groupings. Skipped 5 excess words of a similar stem.