METONYMY

Metonymy is a figure of speech used in rhetoric in which a thing or concept is not called by its own name, but by the name of something intimately associated with that thing or concept. For instance, "Westminster" is used as a metonym (an instance of metonymy) for the Government of the United Kingdom, because it is located there.
Metonymy may also be instructively contrasted with metaphor. Both figures involve the substitution of one term for another. In metaphor, this substitution is based on some specific similarity, whereas, in metonymy, the substitution is based on some understood association (contiguity).
Metonymy works by the contiguity (association) between two concepts, whereas metaphor works by the similarity between them. When people use metonymy, they do not typically wish to transfer qualities from one referent to another as they do with metaphor: there is nothing press-like about reporters or crown-like about a monarch, but "the press" and "the crown" are both common metonyms.
Two examples using the term "fishing" help make the distinction better.The phrase "to fish pearls" uses metonymy, drawing from "fishing" the idea of taking things from the ocean. What is carried across from "fishing fish" to "fishing pearls" is the domain of metonymy.
In contrast, the metaphorical phrase "fishing for information" transfers the concept of fishing into a new domain. If someone is "fishing" for information, we do not imagine that he or she is anywhere near the ocean; rather, we elements of the action of fishing (waiting, hoping to catch something that cannot be seen, probing) into a new domain (a conversation). Thus, metonymy works by calling up a domain of usage and an array of associations (in the example above, boats, the ocean, gathering life from the sea), whereas metaphor picks a target set of meanings and transfers them to a new domain of usage.

Examples

Sometimes, metaphor and metonymy can both be at work in the same figure of speech, or one could interpret a phrase metaphorically or metonymically.For example, the phrase "lend me your ear" could be analyzed in a number of ways. We could imagine the following interpretations:

• Analyze "ear" metonymically first — "ear" means "attention" (because we use ears to pay attention to someone's speech). Now, when we hear the phrase "lending ear (attention)", we stretch the base meaning of "lend" (to let someone borrow an object) to include the "lending" of non-material things (attention), but, beyond this slight extension of the verb, no metaphor is at work.
• Imagine the whole phrase literally — imagine that the speaker literally borrows the listener's ear as a physical object (and the person's head with it). Then the speaker has temporary possession of the listener's ear, so the listener has granted the speaker temporary control over what the listener hears. We then interpret the phrase "lend me your ear" metaphorically to mean that the speaker wants the listener to grant the speaker temporary control over what the listener hears.
• First, analyze the verb phrase "lend me your ear" metaphorically to mean "turn your ear in my direction", since we know that literally lending a body part is nonsensical. Then, analyze the motion of ears metonymically — we associate "turning ears" with "paying attention", which is what the speaker wants the listeners to do.

It is difficult to say which of the above analyses most closely represents the way a listener interprets the expression, and it is possible that the phrase is analysed in different ways by different listeners, or even by one and the same listener at different times. Regardless, all three analyses yield the same interpretation; thus, metaphor and metonymy, though quite different in their mechanism, can work together seamlessly. For further analysis of idioms in which metaphor and metonymy work together, including an example very similar to the one given here, read this article titled Metaphor and Metonymy in Contrast

http://en.wikipedia.org/wiki/Metonymy