Or search: rigor, rigour, badness, asperity, grimness, hardness, hardship, harshness, intensity, sternness, stiffness, raininess, inclemency, severeness, strictness
3 Syllables: SUU
charities, charity, clarity, Hebrides, rarities, rarity, scarcity, verity
4 Syllables: USUU
asperity, austerity, celebrities, dexterity, hysterically, necessities, numerically, severity, vulgarity
5 Syllables: UUSUU
insincerity, unreservedly
6 Syllables: UUUSUU
unpopularity

Found 20 words across 4 groupings.