This is the Sindarin preposition meaning “from”, as well as “of” in the sense “originating from” as in Celebrimbor o Eregion “Celebrimbor of Hollin” [= originating from] (LotR/305). In various phrases where it appears, o seems not to cause any mutation, as with o galadhremmin ennorath “from tree-tangled middle-lands” and o menel “from heaven” (LotR/238). However, in the Quendi and Eldar essay from around 1959-60, Tolkien indicated that this preposition causes stop mutation, which does not mutate voiced stops or nasal m. As Tolkien explained it:

As the mutations following the preposition o show, it must prehistorically have ended in -t or -d. Possibly, therefore, it comes from *aud, with d of the same origin as that seen in Q öar. Some have thought that it received the addition -t (at a period when *au had already become ǭ > o) by association with *et “out, out of”. The latter retains its consonant in the form ed before vowels, but loses it before consonants, though es, ef, eth are often found before s, f, th. [Sindarin] o, however, is normally o in all positions, though od appears occasionally before vowels, especially before o- (WJ/366-367).

A similar etymology (from aut- influenced by et) was given in Definitive Linguistic Notes (DLN) from 1959 (PE17/148). In the Quendi and Eldar essay, Tolkien also said:

*ho as a proclitic might have given o; but it does not occur as a verbal prefix, although it possibly contributed to the Sindarin preposition o (see under *Awa, Sindarin) which is used in either direction, from or to the point of view of the speaker (WJ/370).

Thus in origin this preposition was √AWA “away” + the ancient allative suffix ✶-da “towards”, originally meaning “towards away” = “away from the speaker”, but under the influence of ancient √HO came to simply mean “from” in general, regardless of the direction, either away from the speaker or away from someone or something else.

In the King’s Letter from the omitted epilogue of The Lord of the Rings, this preposition seems to have a definite variant uin in the phrase suilad uin aran o Minas Tirith “the King’s greeting [= greeting from the King] from Minas Tirith”; compare indefinite o “from” later in the same phrase. In this period, in is usually the plural definite article and i is its singular, but in this case the following noun aran is singular. I suspect that for uin this n is epenthetic, used to separate ui = o + i from the following vowel. Compare also definite N. nui = no + i [= “under the”] from The Etymologies of the 1930s (Ety/NU).

Conceptual Development: The earliest precursor of this preposition seems to be G. a(n·) “from” from the Gnomish Lexicon of the 1910s, of which Tolkien said:

a(n·) with vowel mutation = Q ô. “from” {signifying motion} and used as addition to {both} ablative {and allative} cases. Is always suffixed to article in those cases (GL/17).

In Gnomish Lexicon Slips modifying that document, this became G. ô “from” derived from ᴱ✶au̯(a) (PE13/115). The preposition ᴱN. o appeared in some untranslated phrases in the 1920s (PE13/128, 138). In The Etymologies of the 1930s, N. o “from” was derived from the root ᴹ√ƷO “from, away, from among, out of” rather than √AWA, and was equivalent to ᴹQ. ho (Ety/ƷŌ̆).

See S. o for discussion.

See S. o for discussion.

See S. o for discussion.