unknown quantity

Idioms  

1. 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.

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Example Sentences

See Examples For:

unknown quantity

"I was quite pleased with the Branxton animals because that was a bit of an unknown quantity, how well they'd do," he said.

From BBC ● Jul. 7, 2026

But Jon Burrows is much more of an unknown quantity.

From BBC ● Jan. 2, 2026

Humphries, but the veteran is of late something of an unknown quantity.

From Los Angeles Times ● Jun. 20, 2025

Is Levi a professional wildcard—some unknown quantity who requires vetting by the president-elect himself, or someone who demands that his every former employer be contacted by the president-elect himself?

From Slate ● Jan. 9, 2025

This is when I realize that Safer might be what Mom calls an unknown quantity.

From "Liar & Spy" by Rebecca Stead

Related Words

• also-ran
• long shot
• sleeper
• underdog