A noun from the Gnomish Lexicon of the 1910s appearing as G. sinc “metal” (GL/67), clearly the cognate of ᴱQ. sink “mineral, gem, metal” from the root ᴱ√SINI (QL/83).

Neo-Sindarin: I would retain this word for purposes of Neo-Sindarin, but would revise its sense to ᴺS. sinc “mineral”, derived from the primitive form ✶sinki (PE17/108) which may itself mean “*mineral”; see that entry for discussion. I would use N. tinc for “metal”.