Synecdoche
A type of metonymy naming the whole by a part (a sail for a ship) or the part by the whole.
Synecdoche is a particular metonymy based on inclusion: part for whole ("a sail on the horizon" for a ship), whole for part ("France won" for eleven players), singular for plural, material for object ("cold steel").
In narrative it's a framing instrument: choosing which part will stand for the whole is choosing a close-up. Describing a character through "calloused hands" or "polished shoes" selects a different story. A well-chosen synecdoche does the work of a full characterization in one detail.
Example
"A sail on the horizon" (a ship); "hired hands" (workers).