You Pronounce it: [met-uh-nim] IPA:ˈmɛtənɪm
1. A word, name, or expression used as a substitute for something else with which it is closely associated. For example, Washington is a metonym for the US government.
1830-40; back formation from metonymy
I heard it:
In class, the professor asked us to answer a question and used the word “metonym” in the sentence.