The Sindarin noun for “swan” derived from primitive ✶alkwā (NM/378; UT/265; Ety/ÁLAK), where first the [[at|ancient [kw] became [p]]] and then the [[os|[lp] became [lf] (spelled lph)]].
Conceptual Development: In the Gnomish Lexicon of the 1910s, this word appeared as {alcwi >>} alfa (GL/18), which is perhaps the moment that Tolkien decided that labialized velars became labials in the Sindarin branch of Elvish (though in Gnomish this sound change applied only medially). In Gnomish Lexicon Slips modifying this document, the word became alf (PE13/109), and Tolkien stuck with this form thereafter, though eventually revising the spelling to alph once he decide that final [f] was spelled ph. In The Etymologies of the 1930s, N. alf “swan” appeared under the root ᴹ√ALAK “rushing” (Ety/ÁLAK).
n. Zoo. swan.