I am looking for a Latin word corresponding to the common modern English sense of the word "genius", a person with extraordinary ability in a specific field. I do not want to refer to the ability itself (the Latin genius can very rarely mean that; see L&S genius, II.B) but a person in possession of that ability. The Latin word genius is perhaps best translated as "spirit" and does not come close to the meaning I am after.
What would you suggest as a Latin translation of this sense of "genius"?
The ability can be innate or learned. If you suggest a word, can you also describe whether it implies one of these two?
I think this will probably have a different answer than than the question for a translation of "polymath". A genius is great in (at least) one thing, a polymath is good at many things. Same words might be useful for both, but the terms are not synonymous.