Synecdoche

Synecdoche uses a part of something to stand for the whole, or occasionally the whole to stand for a part — 'all hands on deck', 'wheels' for a car, 'Washington' for the government.

All hands on deck. The crew are not hands, and calling them hands does something specific: it reduces them to the part of themselves that is needed. Synecdoche always carries that kind of judgement, which is why it is more than a shortcut.

• Two hundred head of cattle. — animals counted as units.
• He got new wheels. — a car reduced to the part that matters to him.
• She has a good eye. — a whole professional faculty in one organ.

The direction can reverse, with the whole standing for a part: the office decided, when three people decided, or Brazil beat Italy, when eleven players did.

Its close relative is metonymy, which substitutes an associated thing rather than a component part — the crown is not a piece of a monarch. Most handbooks treat synecdoche as a species of metonymy, and in practice nothing turns on which label you use.

In narrative prose it is a reliable way to render a crowd or an institution without a list. A room described as coats, umbrellas, and a smell of wet wool is a room full of people, and the reader assembles them. The choice of part is characterisation of whoever is looking — see show, don't tell.