There is evidence that the later form of this root may have been √ÑGOTH. See ᴺ✶kottō for a discussion.
Another variation, √KHOT “be wroth, quarrel; hate” appears in notes on root formations (PE18/62, 85, 87), but its only derivative ✶ok(h)tā could just as easily come from √KOT(H).
In order to retain all the derivatives from The Etymologies, this entry assumes that the root form remains √KOTH.
This root and similar ones were used for “strife” or “hatred” over Tolkien’s lifetime, but the exact forms varied considerably. One of its more notable derivatives was Q. ohta “war” which Tolkien introduced in the Early Qenya Grammar of the 1920s (PE14/45). However, the earliest precursor of this root was ᴱ√KOSO “strive” from the Qenya Lexicon of the 1910s, but its Gnomish form goth is more representative of its actual primitive form GOÞO (QL/48). At this early stage its most notable derivative was G. Gothmog/ᴱQ. Kosomoko or Kosmot “Strife-and-hatred” (PME/48; LT2/216), but in later writings N. Gothmog was given a new etymology as a combination of ᴹ√GOS “dread” and ᴹ√MBAW “oppress” (Ety/GOS, MBAW).
In The Etymologies of the 1930s the root became ᴹ√KOT “strive, quarrel”, soon revised to ᴹ√KOTH, with derivatives in both Quenya and Noldorin (Ety/KOT). One important new derivative of this root was N. Morgoth “Black Foe”, the first time this name was given a clear etymology, though the name G. Morgoth itself dates back to the earliest Lost Tales (LT2/67). In the first version of the Tengwesta Qenderinwa (TQ1), also written in the 1930s, Tolkien gave ᴹ√KHOT “be wroth, quarrel” as the basis for ᴹQ. ohta “war” (PE18/62). The root form √KHOT also appeared in the second version of the Tengwesta Qenderinwa (TQ2) written around 1950, in one place as revision of a deleted form √KOT; the gloss likewise was changed from “be wroth, quarrel” to “hate” (PE18/85 note #72, PE18/87 and note #77).
In the Outline of Phonology (OP2), Tolkien described a new etymology for the name of Morgoth, basing it on ancient ✶Moriñgotho “Black Foe” = ✶mori + ✶ñgothō; in “modern” Quenya this came to be Q. Morños/t [þ], pronounced morgos/t (PE19/81). Although Tolkien began composing OP1 in the early 1950s, this particular section was a revision written in red ink and thus was later, and it had some additional changes in green ink which Tolkien used to revise OP2 in 1970 (PE19/81 note #65). As Christopher Gilson suggested, the new etymology was certainly connected to the following passage in the later drafts of the Silmarillion:
> Then suddenly Feanor rose, and lifting up his hand before Manwë he cursed Melkor, naming him Morgoth, the Black Foe of the world. [In an author’s footnote] By that name only was he known to the Eldar ever after. (In the ancient form used by Feanor it was Moriñgotho.) (MR/295).
This new etymology might reflect a change of this root to ✱√ÑGOT(H), but it seems Tolkien was not fully committed to this change in the 1950s and 60s. In the Ambidexters Sentence from 1969 Tolkien switched Q. Moringotto to Morikotto before settling on Melkor (VT49/6). There is also the name S. Thuringud “Hidden Foe” from late Silmarillion drafts (WJ/256) whose final element -gud “foe” may well be derived from √KOT (✱kōt(e)) as suggested by Patrick Wynne (VT49/25). Thus Tolkien seems to have vacillated on the exact form of this root frequently over his lifetime.
Neo-Eldarin: For purposes of Neo-Eldarin, I think it is best to assume this root is √KOT, as this preserves the largest number of attested words as Tolkien wrote them, the only major exception being Moringotto. Likewise, I believe the ancient sense “strife, quarrel” is more compatible with attested words than “hate”.