A person with extensive knowledge or ability in a given subject.
If an expert says it can't be done, get another expert. - David Ben-Gurion
We called in several experts on the subject, but they couldn't reach an agreement.
(chess) A player ranking just below master.
verb
(transitive) To have (something) reviewed or checked by an expert.
The bill in question was one proposing to appropriate from the public moneys of this State $30,000 to pay an accountant for experting the books of the Southern Pacific Company, in furtherance of litigation then pending.