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Synonyms

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.

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

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

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

Why is the letter x used for an unknown quantity in algebra?

From Salon • Jul. 29, 2024

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

From "Liar & Spy" by Rebecca Stead

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.