A verb in the Gnomish Lexicon of the 1910s glossed “wash”, marked with a “✱” indicating it also served as a primitive root ✱ᴱ√FASA (GL/34).
Gnomish
thas-
verb. to shave
thas
pronoun. thy
cautha-
verb. to shave
fas-
verb. to wash
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
A verb appearing as G. thas- “shave” in the Gnomish Lexicon of the 1910s (GL/72). It seems to have replaced a rejected word G. cautha- “shave” (GL/24).
Neo-Sindarin: I would retain ᴺS. thas- “to shave” for purposes of Neo-Sindarin as a derivative of the Neo-Root ᴺ√THATH “shave”, where the s is the result of dissimilation away from the initial th. Given the rarity of Elvish beards, this word probably originally applied to shaving the surface of wood.