Ainu noun "holy one, angelic spirit"; fem. Aini (AYAN, LT1:248); "one of the 'order' of the Valar and Maiar, made before Eä"; pl. Ainur is attested. Adopted and adapted from Valarin ayanūz(WJ:399). In the early "Qenya Lexicon", ainu was glossed "a pagan god", and aini was similarly "a pagan goddess", but as Christopher Tolkien notes, "Of course no one within the context of the mythology can call the Ainur 'pagan' " (LT1:248). Ainulindalë noun "Music of the Ainur" (SA:lin #2), the First History (WJ:406), the Song of Creation (AYAN)
holy one, angelic spirit
it is said
-r nominative plural ending regularly used on nouns ending in -a, -i, -ië, -o, -u, e.g. Ainur, Valar, tier. Occasionally it is added also to nouns ending in -ë (that normally take the ending -I in the pl.). This seems to regularly happen in the case of nouns in -lë (see #fintalë, mallë, tyellë), sometimes also otherwise (see Ingwë, wendë, essë #1). This plural ending was ("it is said") first used by the Noldor (PM:402).