What does the idiom "by definition" mean?

Are you using the idiom by definition but not sure about its meaning? Using idioms, which are important elements of spoken and written language, in the right place strengthens your language skills. Examine the meaning of the by definition idiom and the situations in which it is used.

Meaning of "by definition"


The phrase “by definition” is generally used to refer to something that is exactly as it is described, according to its dictionary definition or established set of rules. It implies that the thing being discussed is unambiguous and there is no room for misunderstanding. The phrase is often used to check that both parties in a conversation clearly understand each other.


The phrase “by definition” has been used in the English language since at least the mid-19th century. It comes from the Latin phrase “de definitio” which translates as “of defining”. This phrase is thought to have been used to refer to a definition of a term or phrase and was used to express certainty in understanding.


The phrase “by definition” is used to make a statement more precise. For example, it can be used to show that something is definitively true, or that someone understands the exact definition of something. It can also be used to check that two people are discussing the same thing, or to say that a statement is true beyond a reasonable doubt.

Example Sentences

  • I know what the word means ‘by definition’.
  • By definition, a square is a four-sided shape with all sides equal.
  • This must be done correctly ‘by definition’.

The meanings of the words in the "by definition" 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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