2 Syllables: SU
biggest, bigot, billet, biscuit, Bishop, Bridget, Christmas, citrus, dearest, digit, dimness, fittest, frigate, grimace, hillock, image, inches, India's, Indus, interests, isthmus, limit, lineage, linkage, listless, millet, minute, minutest, mistress, nearest, Nicholas, nitrous, Philip, pickets, pivot, Plymouth, princes, quibus, richest, rivet, simplest, sinless, sinuous, spinach, spirit, syrup, thickets, ticket, vicious, viscous, wicket
3 Syllables: USU
ambitious, Archbishop, assiduous, auspicious, bacillus, capricious, deliberate, delicious, distinctness, elicits, exhibits, explicit, factitious, fictitious, illicit, implicit, inhibit, judicious, malicious, Narcissus, nutritious, officious, Olympus, pernicious, prestigious, prodigious, prohibit, propitious, religious, seditious, severest, sincerest, suspicious, utilise
4 Syllables: UUSU
adventitious, avaricious, expeditious, ignominious, injudicious, irreligious, superstitious, surreptitious, unpropitious, unsuspicious
Found 95 words across 3 groupings. Skipped 18 excess words of a similar stem.