An expression in the usage of a language that is peculiar to itself either in having a meaning that cannot be derived from the conjoined meanings of its elements or in its grammatically atypical use of words.
Idiom:
pitch-black
Meaning:
to be very black
Example:
It was pitch-black when we left the restaurant to return home.
List of common idioms, their meanings and examples of their usage in sentences
An idiom is a type of phrase or expression that has a meaning that can't be deciphered by defining the individual words.