synecdoche

A form of rhetoric in which the word for a part of an thing is used to refer to the whole thing, or the word for the whole is used to refer to the part. It can also be the word for the material for the thing, the class for the subclass, the subclass for the class, etc.

Part for the whole :
'Computer' is usually used as a synecdoche for a computer, keyboard, and monitor ensemble.
'Nice set of wheels' really means 'nice car'.
'20 head of cattle' really means '20 whole cattle'

Whole for the part :
'America' (two whole continents) is used to refer the U.S.A.
'The government keeps taking all my money' is actually a complaint about the IRS.
'We the People' originally used 'people' to refer to white male land owners.

The material for the thing:
'pigskin' for a football.
'Give me some skin' for 'give me {a slap with} your hand'.

From the Greek from synekdekhesthai, meaning 'to supply a thought (or word)'. Rather confusingly, Synekdekhesthai was built out of the words syn- ('with'), -ek ('from' or 'out of'), and dekhesthai ('to receive'). Those Greeks were rather weird.

Pronounced si-nek-duh-kee, rhymes with select-a-key. Sometimes spelled syndoche.

See also Metonymy

Syn*ec"do*che (?), n. [L. synecdoche, Gr. , fr. to receive jointly; with + to receive; out + to receive.] Rhet.

A figure or trope by which a part of a thing is put for the whole (as, fifty sail for fifty ships), or the whole for a part (as, the smiling year for spring), the species for the genus (as, cutthroat for assassin), the genus for the species (as, a creature for a man), the name of the material for the thing made, etc.

Bain.

© Webster 1913.