An idiom is defined as - a group of words whose meaning is different from the meanings of the individual words.
Idiom:
take (someone) into one's confidence
Meaning:
to tell a secret to someone and trust that person to keep the secret
Example:
The bank manager took the customer into his confidence and told him about the banking problems.
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.