hwiniol (giddy; literally this is the participle ”whirling”), lenited chwiniol. It is unclear whether Sindarin participles have any distinct plural forms.
Noldorin
chwiniol
adjective. whirling, giddy, mad, fantastic
chwiniol
noun. whirling, giddy, fantastic
A word appearing N. chwiniol “whirling, giddy, mad, fantastic” in The Etymologies of the 1930s, an adjectival form of N. chwinia- “twirl, whirl, eddy” (Ety/SWIN; EtyAC/SWIN). The gloss “mad” was missing from The Etymologies as published in The Lost Road (LR/388) but was noted by Carl Hostetter and Patrick Wynne in their Addenda and Corrigenda to the Etymologies (VT46/16).
Neo-Sindarin: Most Neo-Sindarin writers adapted this word as ᴺS. hwiniol “whirling, giddy, mad, fantastic” since ancient initial sw became hw in Sindarin of the 1950s and 60s rather than chw as it did in Noldorin of the 1930s and 40s.