A neologism for “frost”, cognate of Q. nixë of the same meaning (WJ/417), that assumes a phonetic development similar to that of S. ach vs. Q. akse (axë) “neck” (PE17/92); see the entry on how [[os|[p], [t], [k] spirantalized before [s]]] in (Old) Sindarin.
Quenya
nixë
frost
nixë noun "frost" (WJ:417); previously described as a synonym of niquis "ice-flake or snowflake", q.v. (PE17:168)