SUBSTITUTION

Rhetorical substitution.

What is the difference between metonymy and synecdoche? vs metaphor

In practice, there isn't much difference: you could arguably pick just one of the terms and use it to describe both types of rhetorical substitution. (I like metonymy: it's easier to spell, more spelling checkers know it, and the meaning is more apparent to me: meta+name.)

“Synecdoche” and “metonymy” are figures of speech in which one thing is used to represent another. In both of these rhetorical figures, the original term and the substitute are closely identified or associated with each other.

In this respect, “synecdoche” and “metonymy” are different from “metaphor,” in which the terms are unrelated yet imaginatively similar (as when you call your ’67 Pontiac “a boat”).

With, “synecdoche,” a part is used to represent the whole or vice versa. Examples commonly cited are the use of “hand” to mean a sailor and “the cavalry” to mean a single trooper. It’s pronounced sin-EK-duh-kee and ^[♦]comes from a Greek word meaning “to take with something else.” (“Schenectady,” the ninth-largest city in New York State, is pronounced skuh-NEK-tuh-dee.)

With “metonymy,” the substituted word is not a part (or an extension) of the original but something associated with it. Classic examples are “the crown” to represent the monarchy and “the sword” to represent military power. It’s pronounced met-ON-uh-mee and comes from a Greek word meaning “change of name.”

Here’s a simple illustration of the difference. A new guy at the office might be described as “a new face” (synecdoche) or as “a new suit” (metonymy).

Metonymy -- using a vaguely suggestive, physical object to embody a more general idea: CROWN for royalty. We use metonymy in everyday speech when we refer to the entire movie-making industry as a mere suburb of L.A., "Hollywood," or when we refer to the collective decisions of the United States government as "Washington," or the "White House." 

Metonymy refers to replacing a word or phrase in a statement with a concept that is closely related. For example, pens are associated with writers, and when Thomas Paine wrote that “The pen is mightier than the sword,” he really meant that the power of words and writers was greater than that of military power. Many examples of metonymy rely on the expectation that people will understand the reference, which is why foreign examples of metonymy sometimes seem utterly mysterious or even laughable.

* The PEN is mightier than the SWORD
* If we cannot strike offenders in the heart, let us strike them in the wallet.