metonymy v. synecdoche

Metonymy is a figure of speech wherein a phrase is substituted with a closely associated concept, e.g., calling the news media ‘the press’ or the American film industry ‘Hollywood’ or the ocean ‘the deep’.

Synecdoche is a specific kind of metonomy in which part of something is used to refer to the whole thing (‘Old Blue Eyes’ for Frank Sinatra), or a whole thing is used to refer to one of its parts (‘America’ for the USA). It can also involve substituting the specific for the general (‘Kleenex’ for facial tissue), the general for the specific (‘thief’ for pickpocket), or a material for a thing made from it (‘plastic’ for credit card).

Some people consider synecdoche to be separate from, rather than a subset of, metonomy. When one word refers to another, but isn’t a part of the thing to which it refers, this is metonomy; otherwise, it’s synecdoche.

World Wide Words on metonomy v. synecdoche