Metonymy is the use of a linked term to stand in for an object or concept. You’ll find examples of metonymy used frequently in both literature and everyday speech. You might use it yourself without even realizing it.
Sometimes metonymy is chosen because it’s a well-known characteristic of the concept. A famous example is, "The pen is mightier than the sword," from Edward Bulwer Lytton's play Richelieu. This sentence has two metonyms:
"Pen" stands for "the written word."
"Sword" stands for "military aggression."
Metonyms are members of the figurative language family, so they serve as colorful ways to take the ordinary and dress it up in something poetic or beautiful.