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.
Idiom:
throw a monkey wrench into the works
Meaning:
to cause something that is going smoothly to stop going smoothly
Example:
My friend threw a monkey wrench into our plans to go to the lake for the summer.
List of common idioms, their meanings and examples of their usage in sentences
An idiom is a group of words, or in other words, a phrase that has a meaning other than its literal meaning of the words in it.