An idiom is defined as - a group of words whose meaning is different from the meanings of the individual words.
Idiom:
on the button
Meaning:
exactly on time
Example:
I arrived for the meeting right on the button.
List of common idioms, their meanings and examples of their usage in sentences
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.