Idiom (noun)

1. A group of words established by usage as having a meaning not deducible from those of the individual words.
2. A form of expression natural to a language, person, or group of people.
3. An expression whose meaning cannot be inferred from the meanings of the individual words that make it up.

Origin:

From french idiome, from greek idiōma, from idiousthai, to make peculiar to a people, from idios, peculiar.

Examples:

1. The phrase "to kick the bucket" is an idiom meaning "to die".
2. In English, the idiom "to let the cat out of the bag" means to reveal a secret.
3. The phrase "to break the ice" is an idiom meaning to start a conversation or to overcome shyness or reserve in a social situation.
4. In American culture, the idiom "to hit the nail on the head" means to say or do something that is exactly right or accurate.
5. The phrase "to pull someone"s leg" is an idiom meaning to tease or trick someone.