An idiom is a figurative phrase that, when taken as a whole, has a meaning you wouldn’t be able to deduce from the meanings of the individual words. How do idioms work? Idioms work based on a language’s syntax—the particular order of words or phrases—and can vary depending on what region of a country you’re in. When are idioms used? An idiom is a common word or phrase which means something different from its literal meaning but can be understood because of their popular use. Idioms are not the same thing as slang. The meaning of IDIOM is an expression in the usage of a language that has a meaning that cannot be understood from the combined meanings of its elements (such as up in the air for 'undecided') or in its grammatically atypical use of words (such as give way for 'retreat'). How to use idiom in a sentence. The Makeup of Idioms Learn 100 common idioms with simple meanings and pictures to help you understand them quickly. Idioms are short expressions that do not mean exactly what the words say and make language more colorful and interesting.