In rhetoric, metonymy ( ) is the use of a word for a concept the original concept behind this word is associated with.

Metonymy may be instructively contrasted with metaphor. Both figures involve the substitution of one term for another. In metaphor, this substitution is based on similarity, while in metonymy, the substitution is based on contiguity.

Metaphor example: The ship plowed through the sea (using plowed instead of navigated).

Metonymy example: The sails crossed the ocean (using sails instead of ship with sails).

In cognitive linguistics, metonymy refers to the use of a single characteristic to identify a more complex entity and is one of the basic characteristics of cognition. It is common for people to take one well-understood or easy-to-perceive aspect of something and use that aspect to stand either for the thing as a whole or for some other aspect or part of it.

A few commonly used examples of metonymy are:

word	original use	metonymic use
sweat	perspiration	hard work
dish	item of crockery	a course (in dining)
press	printing press	news media

Cognitively, metonymy is attested in cognitive processes underlying language (e.g. the infant's association of the nipple with milk). Objects that appear strongly in a single context emerge as cognitive labels for the whole concept, thus fueling linguistic labels such as "sweat" to refer to hard work that might produce it.

The word metonymy is derived from the Greek μετωνυμία (metōnymia) "a change of name", from (meta-) "beyond/changed" and (-onymia), a suffix used to name figures of speech, from (onoma), "name" (OED)).