A group of words which have a different meaning when used together from the one they would have if you took the meaning of each word separately.
lead a dog's life
to live a hard life, to work hard and be treated unkindly
My friend has been leading a dog`s life since he started his new job.
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.