A metonym is a word used in place of a closely related word.
A metonym is a form of figurative language. Metonyms closely resemble metaphors, but the thing being represented by a metonym will be a close match. A metonym is often an attribute or a component part of the thing being represented.
Examples of Metonyms
Here are some examples of metonyms (shaded):
After college, he took to the bottle.
(The bottle is a metonym for alcohol.)
Downing Street supports the proposal.
(Downing Street is a metonym for the Prime Minister.)
The top brass is contesting the cuts.
(Top brass is a metonym for the senior officers.)
This is not how it will be portrayed by Fleet Street.
(Fleet Street is a metonym for the British national press.)
The Benefits of Metonyms
Using a metonym is a good way to keep your writing interesting. It's also a good way of showing your readers that you trust them. Look at this example:
Westminster will convene a special session to debate the issue.
(Westminster is a metonym for The Parliament of the United Kingdom.)
By using this metonym, you're trusting your readers to know where UK's parliament is situated or to work it out from context.