Real Dictionary

metonymy in American English
a figure of speech in which the name of one thing is used in place of that of another associated with or suggested by it (Ex.: “the White House” for “the President”)
noun: a figure of speech that consists of the use of the name of one object or concept for that of another to which it is related, or of which it is a part, as “scepter” for “ sovereignty,” or “the bottle” for “strong drink,” or “ count heads (or noses)” for “c

metonymy in British English
noun: the substitution of a word referring to an attribute for the thing that is meant, as for example the use of the crown to refer to a monarch