Synecdoche ("sin-EK-doh-kee") is the rhetorical or metaphorical substitution of a part for the whole, or vice versa.

Examples: when you refer to workers as "hands," you allow a part (the hand) to stand in for the whole (the person). Ditto in counting cattle as "heads."

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.