An invertible root meaning “noble”, itself an extension of √AR (PE17/147). Given its widespread use, Tolkien did not define this root until quite late. Its first clear mention was in Notes on Names (NN) and Quenya Notes (QN), both from 1957. In NN, Tolkien introduced invertible √ARA/RĀ to give an explanation of the element rod in names like S. Rodon “Vala” and S. Finrod, where Tolkien said:
> S raud “tall, high, lofty, eminent”. √ARA, RĀ. Cf. Q aran “king”. Q arta “high” < árată. S raud < form (a)rā́tă (PE17/118).
Earlier in The Etymologies of the 1930s, the second element of N. Finrod was N. rhaud “metal” (Ety/RAUTĀ), whereas ᴹQ. haran/N. aran “king” was derived from ᴹ√ƷAR “have, hold” (Ety/ƷAR). As for the later root √ARA/RĀ, Tolkien gave a lengthier explanation in QN:
> √AR. ARI-, ARA/RĀ, ARAT/ARAN. Original sense probably seen in adverb/preposition ✱ara/ar/ra, beyond, further than. The stems ARI/ARAN/ARAT mean “good, excellent, noble” - differing from √MAN in stating that any one specimen is “good of its kind”, excels, without necessarily implying that others are bad or marred. Hence ari-, good as prefix, ar/ara/aran as prefixes of excellence especially in royal names, aran king. Q arta noble, arato a “noble”, ráta- excel, surpass. S aran, arod (arāta); or raud excellent, noble, eminent (PE17/147).
Thus all these roots, including the extensions √ARAN and √ARAT, were elaborations on the sense “beyond” from base root √AR. The simple root √AR itself had a lengthy conceptual history; see that entry for details. As for ARA/RĀ, the connection between these forms and nobility seems to be firmly established by the late 1950s and afterwards, with primitive element Ara- “noble” mentioned in The Shibboleth of Fëanor from 1968 (PM/344, 363 note #43), and numerous other mentions of derived forms in documents from this period.
A word that, as a preposition, generally means “beside, next [to]” (PE17/71; VT49/25), which became the basis for the conjunction ar “and” (see that entry for discussion).
Conceptual Development: The preposition ar(a) had a long history in Tolkien’s writings. ᴱQ. ar (as-) “to, against, next, on (wall)” appeared in the Qenya Lexicon of the 1910s under the early root ᴱ√ASA (QL/33). The Etymologies of the 1930s has ᴹQ. ara under the root ᴹ√AR “beside, outside” (Ety/AR²). This ara at first had the glosses “without, outside, beside”, and then “without” and “out” were struck through, with a hard-to-read modification written above “out”, perhaps “hard by” according to the editors, so that the final gloss might have been “hard by side, beside” (EtyAC/AR²).
The preposition ar “beside, next” appeared in notes from 1957 as a derivative of √ADA “beside, alongside, by”, where Tolkien said ar “and” was a related adverb (PE17/145). The preposition ar appeared in the first version of the Löa Yucainen from 1958 in the phrase Yénion yukainen nunn’ ar anduine lútie “Years ten and ten have down the Long River floated”, but its exact function is unclear (CPT/1296).
In notes on comparison from around 1964, Tolkien used ar as an alternative to epë “before” in comparative phrases. For example A anamelda na ep’ ilya “A is [dearer] than all others” could also be written A anamelda na __ar__ ilyan (PE17/57); this could be “A is very-bright beside all”, or it could be a variant of superlative ar(i)-. In the same set of notes Tolkien described √ADA as the basis for ar “and”, saying:
> This was in origin a preposition from the √ADA meaning “alongside, by the side of”. In Quenya the simple form ad(ă), ad had ceased to be used as a preposition with this full (physical) sense, except as a prefix (equivalent more or less to English “by-”), as in Arvernien “(the land) beside the Verna” (PE17/71).
Despite the claim that it has “ceased to be used as a preposition”, ara appeared in notes associated with the Ambidexters Sentence from 1969, again derived from ✶ad(a) “beside(s)” (VT49/25). It was part of a prepositional paradigm giving its combination with various pronouns, including arni “✱beside me” and arse “✱beside him”. In a note from 1968, arse appeared in the sentence: (qui)quie menin coaryanna / __arse__ “whenever I arrive at his house/come to/get to, he is out” (VT49/23). This sense “out” might be connected to its gloss “outside” in The Etymologies of the 1930s, or it might be in a privative sense “✱without him” as suggested by Patrick Wynne (VT49/35-36 note #34).
Neo-Quenya: For purposes of Neo-Quenya, I would assume ar(a) as a preposition means “beside, ✱by”, as opposed to conjunctional ar “and”, for example: i atan ar i elda tarne ar i nauco “the man and the elf stood beside the dwarf”. Where the two uses are ambiguous, the longer form ara “beside” can be used. I would not use ara for “outside” except in the limited sense “just outside = next to”; see the prefix ar- for more discussion.