Metonymy is when you substitute an attribute or something closely related to a thing for the name of the thing.
Suit = business man
Crown = monarch/monarchy
Oval Office = presidency/president
Lend a hand = help
pen = written word (i.e. "The pen is mightier than the sword.)
Examples of Metonymy from Literature:
From Margaret Mitchell's Gone With the Wind-Georgia refers to the government, people of Georgia:
"I'm mighty glad Georgia waited till after Christmas before it seceded or it would have ruined the Christmas parties."
From F. Scott Fitzgerald's The Great Gatsby-Fitzgerald uses the place name to stand for the people who live in the place:
"The party preserved a dignified homogeneity, and assumed to itself the function of representing the staid nobility of the countryside-East Egg condescending to West Egg, and carefully on guard against its spectroscopic gayety."
From Shakespeare's MacBeth-table refers to those who are present:
"I drink to the general joy o' the whole table."
From Shakespeare's Julius Caesar-Antony uses "ears" as a way to ask the crowd to listen:
"Friends, Romans, Countrymen, lend me your ears . . ."