Metonymy:
A figure of speech in which the name of one object is substituted for that of another closely associated with it.

Example:
"Her voice is full of money."
-F. Scott Fitzgerald from The Great Gatsby

Explanation:
Fitzgerald uses metonymy by saying "her voice". Her voice is not "her", so it is a metonymy. Fitzgerald does this to describe the woman as someone that only cares or talks about money. This is significant because the novel as a whole has to do with the upper-class and their "clique". This figure of speech used to describe the woman puts a mental picture through the readers head that has a wealthy, snobby women who thinks and talks about money at all times.