Or search: ai, cdc, ins, irs, usa, gao, arda, disa, lieu, navy, nist, noaa, osha, plum, rite
2 Syllables: SU
offerings
3 Syllables: SUU
causative, goddesses, hostages, novices, positive, promises, Solomon's, talkative, Thomas's
4 Syllables: USUU
cooperatives, corroborative, hypothesis, prerogative, provocative

Found 15 words across 3 groupings. Skipped 1 excess word of a similar stem.