Expert

1. An expert or experienced person; one instructed by experience; one who has skill, experience, or extensive knowledge in his calling or in any special branch of learning.
2. Taught by use, practice, or experience, experienced; having facility of operation or performance from practice; knowing and ready from much practice; clever; skillful; as, an expert surgeon; expert in chess or archery.
3. To experience.
4. A specialist in a particular profession or department of science requiring for its mastery peculiar culture and erudition.
5. A sworn appraiser.