unknown quantity

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.

Example Sentences

Raising Cane’s managers make the sauce from unidentified ingredients that are shipped to their locations in bags of unknown quantities.

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This results in the release of unknown quantities of neurotoxins, carbon monoxide and other chemicals into the air.

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The 46-year-old Dutch coach built a fine reputation with successes at Feyenoord, but was an unknown quantity to many Liverpool supporters and untested in the Premier League.

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

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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.

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Related Words

• also-ran 
• long shot 
• sleeper 
• underdog