Well, I had to look up "avidity" because I've never used it. It seems you would have to say "avidity for" not "avidity of," but I'm generally considered to have a pretty good vocabulary, and if I had to look it up, I expect others you say it to might have a hard time understanding your meaning as well. ) A more common word is "affinity" - he has an affinity for knowledge of all types.
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ZeroxWell, for impressiveness, you could toss in an adjective: "unquenchable thirst", or "insatiable hunger", or "untamable passion".
Well, im doing an important essay and i need to impress my teacher