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:
last straw
Meaning:
the last insult or mistake or problem that one can endure and which then causes some reaction
Example:
The fourth time that the girl came to work late was the last straw and we finally fired her.
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.