A name of Men as mortal beings (S/102, WJ/387). It is the adjective fírima “mortal” used as a noun.
Conceptual Development: In Silmarillion drafts from the 1930s, the form of this word was ᴹQ. Fírimo ending with an -o (LR/245). This form also appeared in Fíriel’s Song from the same time period. The form Fírima appeared in the Quendi and Eldar essay from 1959-60 (WJ/387), and this was the form used in the published version of The Silmarillion (S/102).
In later writings, the older form form still appeared, however. The form fírimonnar appeared later in a draft version of Alcar mi Tarmenel na Erun, Tolkien’s partial translation of Gloria in Excelsis Deo from the 1950s, but it was eventually replaced with híni “children [of God]”. Also, fírimor appeared in a draft version of the Ambidexters Sentence from the late 1960s, but it did not appear in the final version. Tolkien seems to have vacillated between Fírimo and Fírima in his later writings, but Fírimo was always replaced with something else, while Fírima was allowed to stand.
fírima adj. "mortal" (PHIR; firima with a short i in VT46:4); also used as noun: Fírima pl. Fírimar "those apt to die", "mortals", an Elvish name of Mortal Men (WJ:387). This adj. is also the source of an explicit noun, personalized #Fírimo = mortal, mortal man. Pl. Fírimor (VT49:10-11), dative pl. fírimoin "for men" in Fíriel's Song; cf. also the pl. allative fírimonnar in VT44:35.