Conceptual Development: The name ᴱN. Thuringwethil first appeared in the Lays of Beleriand from the 1920s, where it was translated “She of Hidden Shadow” (LB/304). In The Etymologies from the 1930s, Thuringwethil was designated a Doriathrin [Ilkorin] name, translated “(Woman of) Secret Shadow”, and apparently had essentially the same derivation as given above (Ety/THUR).
feminine name. Woman of Secret Shadow
Word Gloss thurin “secret, hidden” gwath “shadow, dim light, shadow, dim light, [N.] shade” -il “feminine suffix”