Definition - A word that represents a part of something but which has come to be used to refer to the whole.

Example -
Using the word turf to refer to horse racing in general.

Etymology -
The word derives from the Greek metonymia, a change of name (from the Greek meta, change + onoma, name).

Oxford English Dictionary -
Its first citation is from 1837–8:
"The term testimony, I may notice, is sometimes, by an abusive metonym employed for witness."
(Sir W. Hamilton Logic xxxiii. (1860) II. 177 )

Please comment