Or search: gaiety, jocosity, frivolity, flippancy, merriness, humorousness
3 Syllables: SUU
charity, chemically, chemistry, clarity, effigy, Emily, lenity, rarity, registry, verity, wretchedly
4 Syllables: USUU
aesthetically, aggressively, asperity, austerity, celebrity, confessedly, dexterity, excessively, genetically, hermetically, hysterically, impressively, majestically, necessities, necessity, numerically, obscenity, pathetically, poetically, progressively, severity, successively, summarily, symmetrically, vulgarity
5 Syllables: UUSUU
alphabetically, biochemistry, diametrically, energetically, geometrically, infidelity, insincerity, parenthetically, sympathetically, theoretically
6 Syllables: UUUSUU
apologetically, unpopularity

Found 48 words across 4 groupings.