A root appearing in notes on words and phrases from The Lord of the Rings from the late 1950s or early 1960s, serving mainly as the basis for S. naith “angle” (PE17/55). It was also mentioned in a discussion of the death of Isildur at the Gladden Fields, again as the basis for S. naith among other words, where the root √NEK was glossed “narrow” (UT/281-2, note #16). In The Etymologies of the 1930s, N. naith was derived from ᴹ√SNAS or ᴹ√SNAT, but the precise derivation was unclear, and in any cases seems to have been replaced by Tolkien with a more straightforward derivation from √NEK.
The root √NEK also appeared in Quenya Notes (QN) from 1957 with the gloss “deprive”, serving among other things as the basis for S. neithan “one deprived” (PE17/167), which was the name adopted by Túrin after he became an outlaw (S/200). The root appeared again in notes on Elvish numbers from the late 1960s glossed as either “divide, part, separate” (VT47/16) or “divide, separate” (VT48/9), where it served as the basis for √ENEK “six” as the dividing point between the lower and upper set of numbers in the Elvish duodecimal system.
It is not clear whether Tolkien intended all these various meanings for the root √NEK to be connected. For purposes of analysis, I’ve split √NEK “narrow” from √NEK “separate; deprive”, but conceivably the sense “narrow” could be a semantic extension of “separate” or vice-versa.
A “Sindarin only” root in etymological notes from around 1959-60, whose primary purpose seems to be the derivation of Sindarin words for “vengeance” (PE17/167) as in the phrase tôl acharn “vengeance comes” from contemporaneous Silmarillion narratives (WJ/254), though this phrase didn’t make it into the published Silmarillion. Tolkien explained this root as a blending of prefixal √AT “re- (a second time)” and √OKO “evil”, also seen in the word Q. olca. √AK replaced an earlier derivation of Sindarin vengeance-words directly from the root √AT (PE17/166), which Tolkien may have rejected because this did not have the connotation he wanted: at-kar- = “doing again”, not “revenge”.