Synecdoche
A figure of speech in which a part stands for the whole, or the whole stands for a part.
Synecdoche is a close cousin of metonymy, but the substituted term is a piece of the thing rather than merely something linked to it. Writers use it to make abstract or large ideas feel concrete and immediate. Calling a car “a set of wheels” or workers “hands” are common instances.
Example
The line about lacking “a sail” on the horizon uses sail to mean an entire ship, a part standing in for the whole vessel.
The Rime of the Ancient Mariner · Samuel Taylor Coleridge
Related terms
MetonymyA figure of speech that names something by referring to a closely associated thing rather than the thing itself.ImageryDescriptive language that appeals to the senses to create vivid mental pictures.MetaphorA comparison that calls one thing another to suggest a shared quality, without using like or as.