A noun appearing as G. fidhra “collective hair” in the Gnomish Lexicon of the 1910s (GL/35) clearly derived from the early root ᴱ√FIŘI [FIÐI] (QL/38). It may refer to “✱all hair on the body” given its elaboration G. fidhrad “hairy, hirsute”.
Neo-Sindarin: I would adapt this word as ᴺS. fidhras, generalized from the adjective ᴺS. fidhren “having hair”.
A noun in the Gnomish Lexicon of the 1910s glossed “hair, long tresses”, a term Tolkien said was used especially of women (GL/33). Its primitive form appearing on another page as ᴱ✶fīđ’lī (GL/35). Its form illustrates a number of Gnomish sound changes, notably how long ī became ai and how ðl became gl; these sound changes were abandoned in later Sindarin.