This root was the basis for Elvish words for “counting” for much of Tolkien’s life. The earliest indications of the root are in primitive ᴱ✶notta > ᴱN. noth “number” in Early Noldorin word lists of the 1920s, along with related words like ᴱN. gonod- “count” (PE13/145, 151); the revision of noth “number” to nath may represent some uncertainty on its initial form, but it seems Tolkien restored noth in a marginal note (PE13/150, 151).
The root reappeared as ᴹ√NOT “count, reckon” in The Etymologies of the 1930s with a number of derivatives of similar meaning, the most notable being N. arnœdiad or arnediad “innumerable, countless, endless” (Ety/NOT) as in Nirnaeth Arnoediad “[Battle of] Tears Unnumbered”, a name Tolkien introduced in the 1930s and with minor variations (Nirnaith vs. Nirnaeth, Arnediad vs. Arnoediad) retained thereafter. The root √NOT itself appeared several times in Tolkien’s later writings (PE17/62; PE19/86), most notably as the basis for Q. únótima “numberless” from the Q. Namárië poem (LotR/377).