†Ó noun "the sea" (poetic word, hardly valid in Tolkien's later Quenya) (LT1:263, there spelt Ô)
Quenya
ó
preposition. [together] with
ó
the sea
ó
with, accompanying
ó-
used in words describing the meeting, junction, or union of two things or persons, or of two groups thought of as units
ó- (usually reduced to o- when unstressed) a prefix "used in words describing the meeting, junction, or union of two things or persons, or of two groups thought of as units". In omentië, onóna, ónoni, q.v. _(WJ:367, PE17:191; in the Etymologies, stem WŌ, the prefix _o-, ó- is simply defined as "together".) In VT43:29 is found a table showing how pronominal endings can be added to the preposition ó-; the resulting forms are onyë or óni "with me", ómë "with us" [also in VT43:36, where "us" is said to be exclusive], ólyë or ólë "with you" (olyë only sg. "you", whereas ólë can be either sg. or pl.), ósë "with him/her", ótë *"with them" (of animates where "them" refers to non-persons, óta [or shortened ót] is used, though the conceptual validity of ta as a pl. pronoun is questionable), ósa (or shortened ós) "with it". (Two additional forms, ótar and ótari, presumably mean "with them" of inanimate things; see VT49:56 for a possible second attestation of tar as the word for plural inanimate "they".) However, Tolkien's later decision to the effect that ó- refers to two parties only may throw doubt upon the conceptual validity of some of these forms, where at least three persons would be implied (like ótë "with them", where one person is "with" two or more others though Tolkien indicates that two groups may also be involved where the preposition ó- is used). The explicit statement in WJ:367 that the prepostion o (variant of ó) did not exist independently in Quenya is however difficult to get around, so instead using the preposition ó/o (with or without endings) for "with", writers may rather use as, the form appearing in the last version of Tolkien's Quenya Hail Mary (also attested with a pronominal suffix: aselyë "with you").
o-
prefix. together
A prefix meaning “together” derived from primitive √WO (WJ/367). The modern Quenya form of the prefix is the result of the sound change whereby “unstressed wo was often reduced to o with loss of w” (PE19/106). Note that “when stressed the [primitive] sequence wo was usually changed > wa”, so in theory Quenya might have a variant prefix ✱va- “together” that was the result of an ancient stressed prefix, much like Sindarin go- vs. gwa-. However, there is little sign of such a prefix va- in Quenya; the only example is vávea “(con)similar”. Instead, the short o- generally became ó- in those rare cases where it was stressed (WJ/367).
In the Quendi and Eldar essay from 1959-60 Tolkien said that o- was “used in words describing the meeting, junction, or union of two things or persons, or of two groups thought of as units”, as opposed to yo- used for three or more things (WJ/361, 367). In examples elsewhere, though, o- “together” seems to have a more general meaning in words like olass(i)ë “foliage, collection of leaves” or ombari “company, dwellers together” (NM/117). I would therefore assume yo- is only used when plurality was emphasized, and o- “together” was the default choice otherwise.
Conceptual Development: The earliest precursor to this suffix appeared in the Gnomish Lexicon of the 1910s as ᴱQ. ma- “together” derived from primitive ᴱ✶ŋu̯a (GL/40). This was part of a paradigm in which G. go- was the result of unstressed ᴱ✶ŋu̯a, and gwa- was the normal phonological result. There was also an apparently related suffix ᴱQ. -ngwe in the Narqelion poem in phrases like ómalingwe lir’ amaldar = “✱(together) with voices singing gently”, which could also be derived from primitive ᴱ✶ŋu̯a. The Early Noldorin Dictionary of the 1920s had ᴱQ. va- as the equivalent of ᴱN. go- “together”, probably reflecting a change to primitive ✱wa- (PE13/162).
The Etymologies of the 1930s had both ᴹQ. ō̆- and N. go- “together” derived from the root ᴹ√WŌ̆ (Ety/WŌ). In this new paradigm, N. gwa- was the result of stressed primitive wó-. In Quenya primitive wō and unstressed wŏ blended to produce o- “together”, which could be either short o or long ó. In the Outline of Phonetic Development (OP1) of the 1940s, Tolkien seems to hint that stressed (g)wo- > wá- in Quenya as well (PE19/53). But as noted above there is only one example (vávea) of prefixal wa-/va- “together” in actual Quenya words from Tolkien’s later writings.
vá meninyë ó le
I won’t come with you
The preposition ó “with” appeared in draft versions of the Aia María prayer from the 1950s, in the phrase i Héru olesse “the Lord is with thee” (VT43/27), along with a chart for this preposition having pronominal suffixes (VT43/29). Prepositional ó is clearly related to the prefix o- “together”. In the third version of the prayer, it was revised to carelye (VT43/27), apparently a variant of the preposition ca as suggested by Wynne, Smith, and Hostetter (VT43/29). In the fourth and final version of the prayer it became aselye (VT43/28), using an otherwise unattested preposition possibly related to √AS “beside”.
In the Quendi and Eldar essay of 1959-60, Tolkien said of primitive WO “together” that it “does not remain in Q as an independent word” (WJ/367). However, the preposition ó “with” reappeared in a phrase from 1969: vá meninye {yó >>} ó le “I won’t come with you” (PE22/162). Based on the revision of {yó >>} ó and the meaning of the related prefixes, it is likely that ó more specifically means “with (one other individual)” as opposed to yó(m) for “with (a group)”. However, I think ó could be used in most cases, and yó(m) is only used when accompanying a group is being emphasized.
Neo-Quenya: It seems likely that ó specifically means “[together] with”, and other senses of “with” would use other prepositions such as lé “with, by (means of)” or the instrumental suffix -nen.