Synecdoche is a figure of speech which substitutes a whole object with one aspect of that object. It may also be used to replace a specific object with something more generalized. A kind of imagery, synecdoche is often used in both poetry and prose, as well as in casual speech and slang. The term is nearly identical to the Greek word in which it was derived, synekdoche, which means "simultaneous understanding."
Often used to characterize and control imagery, synecdoche is employed by authors and the casual conversationalist alike. In synecdoche, a specific part of an object is understood to mean the whole object. For example, saying "the talon swooped down upon its prey," replaces a bird of prey with one aspect of that bird: its talon. In this case, the device is most likely used to control the image of the bird in the reader's mind. Drawing attention to a single clawed foot, the exact appendage engaged in the act rather than the bird as a whole, the technique serves as a sort of written close-up.
Synecdoche is also used to dehumanize. The sentence "I saw the hand that murdered her" removes the human aspect from the act, reducing the murderer to a mere appendage. This dehumanization occurs, often innocently, in casual conversation as well. The popular term "head count," used to refer to the number of people in a given group, replaces a human being with one physical attribute: the head. In so doing, it is clear that a "head count," though referring to individuals, is not actually about people but about numbers.
Additionally, synecdoche can be found in slang, such as referring to a car as "wheels." In the case of slang and casual conversation, most users are not aware they are using synecdoche and do not do so for any intentional dramatic effect. Authors may or may not be consciously aware of this figure of speech when they employ it, but usually they hope to achieve the dramatic effects it creates.
Synecdoche may also be used to refer to a specific object by using a larger or more generalized object. For example, the term America may refer to the continent of South America or the continent of North America. The term is often used to mean the United States, however, which is only one part of North America. In order to be used in this way, the larger object must include, but not be limited to, the specific thing it is referencing.