1590s, in the argot of petty criminals; probably aphetic of abet, or from obsolete beet "to make good," from O.E. bætan "make better, arouse, stimulate," from P.Gmc. *baitjanan. The original notion is perhaps "to improve" a contest by wagering on it, or it is from the
interj. Yes.; You can bet on it. : Can you have two? You bet.
Dictionary of American Slang and Colloquial Expressions by Richard A. Spears.Fourth Edition. Copyright 2007. Published by McGraw Hill.
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