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Know your onions

Posted by ESC on May 30, 2003

In Reply to: Know your onions posted by Gary on May 30, 2003

: I can't find a definitive source for this. Any ideas?

I've heard it before and feel pretty confident that it's a Southern (U.S.) expression. "He really knows his onions." Meaning he is an expert in something.

From the archives:

ONIONS - (plural noun) business, affairs. 1954. W.G. Smith South St. 297: You just sit here, tend to your onions, let me handle the people what cross me. From the "Random House Historical Dictionary of American Slang, Volume 1, H-O" by J.E. Lighter, Random House, New York, 1994.

Why onions? Mr. Lighter doesn't say. Another definition for "onion" in the same reference is "the head" as in "off one's onion."

While I was looking for "knows his onions" I found this phrase. Doesn't have anything to do with onions, but interesting still:

KNOW ONE'S CANS - "Cowboys on the range in the 19th century were usually starved for reading matter and often read the labels on the cook's tin cans, learning them by heart. A tenderfoot could always be distinguished because he didn't know his cans." From "Encyclopedia of Word and Phrase Origins" by Robert Hendrickson (Facts on File, New York, 1997).