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:
not bat an eye
Meaning:
to not show any signs of being nervous even when something shocking or bad happens
Example:
The policeman did not bat an eye when the criminal began to reach for his knife.
List of common idioms, their meanings and examples of their usage in sentences
Idioms are phrases which cannot be understood simply by looking at the meaning of the individual words in the phrase.