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

The real Colbert, not the character, would helm the show, and that guy behind the mask was still an unknown quantity to the viewing public.

From Los Angeles Times ● May 20, 2026

Mr Barrington said Wolves of Wiltshire have specific licenses that allow them to care for the animals, because they were an "unknown quantity, and they could have potentially required a dangerous animals license".

From BBC ● Jan. 11, 2026

Reform are still a relatively unknown quantity in Scotland, and their swift rise to prominence is a factor that could make that election fairly unpredictable.

From BBC ● Jun. 5, 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

Doubleday an unknown quantity, but certainly nothing spectacular.

From "The Killer Angels: The Classic Novel of the Civil War" by Michael Shaara

Related Words

• also-ran
• long shot
• sleeper
• underdog