The Gnomish Lexicon of the 1910s had a word thastril “razor”, an elaboration of G. thas- “shave” (GL/72). It also had (unglossed) G. thasgim probably of the same meaning, a combination of G. thas- “shave” and G. cim “blade” (GL/26).

Neo-Sindarin: Since I retain both ᴺS. thas- “shave” and ᴺS. cim “blade” for purposes of Neo-Sindarin, I would use ᴺS. thasgim for “razor”.