A word appearing as G. cuithos “life (period of life); living, livelihood” in the Gnomish Lexicon of the 1910s, a noun form of G. cuitha- “am alive” (GL/27).
Neo-Sindarin: For purposes of Neo-Sindarin, I’d update this word to ᴺS. cuithas using the later abstraction noun suffix -as, and would assume it is an abstraction based on ᴺS. cuith “[biological process of] life”. I would use it to refer both to the means of providing for one’s life (= “livelihood”) as well as a period of time within one’s life, as opposed to one’s entire lifetime which would be ᴺS. cuilvorn.
A word appearing as G. cuith in the Gnomish Lexicon of the 1910s with glosses “life, the vital principle” and “a living body”; Tolkien specified that it was never used for “a lifetime”, which was instead G. cuil (GL/27). It was likely based on the early root ᴱ√KOẎO “have life” as suggested by Christopher Tolkien (LT1A/Koivië-néni).
Neo-Sindarin: For purposes of Neo-Sindarin, I’d retain ᴺS. cuith as “life, the vital principle” in reference to the biological process of life and being alive. For “life” in its more ordinary sense I’d use [N.] cuil.