An idiom is a phrase that does not have the same meaning as the literal meaning. Often it is a phrase or cliche that has been adopted as common use in a language. The phrase "cat on a hot tin roof" is an example of an idiom....
“What is that?” said Dr. Carr, who had just come in, and was on his way up stairs. “It sounds as if it came from the attic,” said Mrs. Carr (for this was before Mamma died). “Can it be that one of the children has got out of bed and wandered up stairs in her sleep...