Sindarin 

belaith

adjective. mighty

An adjective for “mighty” derived from the root √MBELEK in a page of notes having to do with “large & small” words, probably from the late 1960s (PE17/115), apparently from the primitive form ✱✶mbelektā with the ekt vocalizing to eith and then the ei becoming ai in the final syllable.

Sindarin [PE17/115] Group: Eldamo. Published by