Etymology

From the Greek, "change of name"


Another examples are :

Crown - in place of a royal person

The White House - in place of the President or others who work there

Ears - for giving attention ("Lend me your ears!" from Mark Antony in Julius Caesar)

Pen - for the written word

Sword - for military might

Silver fox - for an attractive older man

Purpose of a Metonymy

As with other literary devices, one of the main purposes of using a metonymy is to add flavor to the writing.

Using a metonymy serves a double purpose - it breaks up any awkwardness of repeating the same phrase over and over and it changes the wording to make the sentence more interesting.

Difference Between Metonymy and Synecdoche

Definition

Metonymy is a figure of speech in which something is introduced by a new name that is related to the original thing or concept.

Synecdoche is a figure of speech where a word or phrase that refers to a part of something is used to represent the whole or vice versa.

New Term

Metonymy uses a related name or concept.

Synecdoche uses a part to represent the whole or vice versa.

Examples

Metonymy examples mostly include proper nouns.

Synecdoche examples often include common nouns, especially body parts.

Reference :

http://examples.yourdictionary.com/examples-of-metonymy.html

http://pediaa.com/difference-between-metonymy-and-synecdoche/