√AK root. “hostile return”
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”.
References ✧ PE17/145, 167