IDIOMS

An idiom is a group of words in current usage having a meaning that is not deducible from those of the individual words. For example, “to rain cats and dogs” - which means “to rain very heavily” - is an idiom; and “over the moon” - which means “extremely happy” - is another idiom. In both cases, you would have a hard time understanding the real meaning if you did not already know these idioms!