An idiom is defined as - a group of words whose meaning is different from the meanings of the individual words.
Idiom:
at death's door
Meaning:
to be near death
Example:
The young woman was at death's door after the accident.
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.