A noun appearing as G. beg “chin” in the Gnomish Lexicon of the 1910s, along with a more elaborate form G. bectha “tip; chin” and (deleted) G. begl “beard” (GL/22). Tolkien connected the word G. beg “chin” to ᴱQ. pē “mouth” (GL/22) and not to ᴱQ. venta “chin” from contemporaneous the Qenya Lexicon of the 1910s under the early root ᴱ√VETE (QL/101).
Neo-Quenya: It is hard to reconcile either beg or bectha with primitive forms from later iterations of the languages, so I’d instead coin a neologism ᴺS. bened “chin” for purposes of Neo-Sindarin, cognate of ᴺQ. venta “chin” and derived from a Neo-Root ᴺ√BENET based on ᴹ√BEN “angle”.