Metonymy ("met-AH-na-mee") is the rhetorical or metaphorical substitution of a one thing for another based on their association or proximity.

Examples: a monarch is not the same thing as a crown, but we often refer to the monarch as "the crown" because the two are associated. ???

From the Guide to Literary Terms by Jack Lynch.
Please send comments to Jack Lynch.
Note: This guide is still in the early stages of development.
Three question marks mean I have to write more on the subject. Bear with me.