n. a professional (at anything); someone as good as a professional. : When it comes to typing, he's a pro.
Dictionary of American Slang and Colloquial Expressions by Richard A. Spears.Fourth Edition. Copyright 2007. Published by McGraw Hill.
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Word Origin & History
pro
1866, shortening of professional. The adj. is first recorded 1932. Pro-am "including professionals and amateurs" is from 1949.