When this root first appeared in The Etymologies (Ety/PHAY), it was glossed “radiate, send out rays of light” and its derivatives were consistent with this definition, most notably in N. Feanor “Radiant Sun”. In later writings, this root was instead glossed “spirit” (PM/352), which is the connotation of most of its later derivatives. For example, the later meaning of S. Fëanor was changed to “Spirit of Fire”.
The earlier sense “radiate” probably also survived in Tolkien’s later conception, however. On MR/250, the word Q. fairë “spirit” is said to originally have had the sense “radiance”, which is precisely the meaning that ᴹQ. faire had in The Etymologies. There is also a primitive monosyllable ✶phāy “flame, ray of light” in the Outline of Phonology from the early 1950s (OP2: PE19/102). If the root meaning “radiate” remains valid, then the word S. ✱fael “gleam of the sun”, an element of S. Faelivrin “gleam of the sun on the pools of Ivrin” (the second name of Finduilas), might be a derivative of this root.
A noun translated “spirit” and fully declined as an example of a Weak II noun (SD/438). It appeared with both a short a (SD/424) and long â (SD/438). Given its ending -ô, it might be a masculine-noun, but it seems unlikely that spirits would only be male. This entry assumes it is a common-noun instead. It is probably related to ᴹQ. manu “departed spirit” as suggested by various authors (AAD/19, AL/Adûnaic, EotAL/MAN).