What does the idiom "an unknown quantity" mean?

The expression an unknown quantity is one of the idioms that often finds a place in our literature and enriches our language. However, its meaning is not fully understood, so it is sometimes used in the wrong situations. Please review the explanation carefully for the correct use of the an unknown quantity idiom.

Meaning of "an unknown quantity"


The phrase “an unknown quantity” is used to describe a person or thing whose characteristics, abilities, or value cannot be accurately determined or predicted. This phrase often carries the implication that the person or thing in question is an unknown risk, and that their involvement in a situation may be likely to bring uncertain or difficult outcomes. This phrase can also refer to an unpredictable or indefinite event.


The phrase “an unknown quantity” originated in the early 19th century with the use of the phrase in mathematics. In mathematics, an unknown quantity is a value or quantity whose existence or value is not known at the time of calculation, typically represented by a letter or symbol. This concept is used in algebraic equations and in other situations where a variable needs to be evaluated before its result can be determined.


This phrase is typically used to refer to a person or thing whose characteristics, abilities, or value cannot be accurately determined or predicted. It may also be used to describe an unpredictable event or outcome. This phrase can also refer to a situation where there is a lack of knowledge or information.

Example Sentences

  • He is an unknown quantity, so we don't know how he will react in this situation.
  • The outcome of this election is an unknown quantity; no one can predict who will win.
  • Investing in a start-up company is always an unknown quantity, so it's best to proceed with caution.
  • He's a wild card, an unknown quantity that you can never predict.

The meanings of the words in the "an unknown quantity" idiom

Beyond the Literal: Figurative Language in Idioms

Idioms often use figurative language to convey a message that is not meant to be taken literally. For instance, the idiom "bite the bullet" means to endure a painful or difficult situation without complaint, while "hold your horses" means to be patient and wait. Other idioms, like "kick the bucket" or "pop your clogs," use euphemisms to talk about death.


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