unknown quantity
Idioms & Phrases
unknown quantity
An unpredictable person or thing, as in We don't know how the new pitcher will do
he's an unknown quantity. This expression comes from algebra, where it signifies an unknown numerical value. Its figurative use dates from the mid-1800s.
The American Heritage® Dictionary of Idioms by Christine Ammer.
Copyright © 1997. Published by Houghton Mifflin.
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Copyright © 1997. Published by Houghton Mifflin.
Cite This Source
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