According to WJ/366, the preposition "is normally o in all positions, though od appears occasionally before vowels, especially before o-". With a suffixed article, see also uin
Noldorin
manwe
masculine name. Manwe
ar vanwe
proper name. Day of Manwe, first day of the Valian week
a
conjunction. and
ar
conjunction. and
balan
noun. Vala, divine power, divinity
o
preposition. from, of (preposition (as a proclitic) used in either direction, from or to the point of view of the speaker)
The Noldorin name for the 1st day of the Valian 5-day week, a combination of the prefix ar- “day” and the lenited form of Manwe (Ety/AR¹, LEP).