Here is what Ales Bican suggests for Aaron (at his site ELM). This is Quenya:
AARON - perhaps Heb. 'enlightened one'; nóla "wise, learned", quen "one", so Nólaquen.
From a quick look at various websites I have found a number of only possible meanings. Here is but one entry, which also contains 'mountain' at least: 'From the Hebrew name (...) which is most likely of unknown Egyptian origin. Other theories claim a Hebrew derivation, and suggest meanings such as "high mountain" or "exalted".
Anyway, considering the general conclusion that the meaning is unknown for certain, I'm not sure you can necessarily be wrong with any of them.
Perhaps *Orontar 'Mountain' plus -tar 'high', as in 'exalted' [if we may use it this way as a suffix that is, as at the moment I can't recall other examples] -- as a prefix compare Tolkien's Tareldar 'High Elves'.
Not perfect, but not nothing
