Metonymy is a rhetorical form referring to a figure of speech in which something is referred to by something closely related to it. It is closely akin to a simile or metaphor, but it not quite the same.
Examples of metonymy include referring to 'the president' as 'the White House' or 'oval office', or 'the Russian government' as 'the Kremlin'. Sometimes sayings such as "they counted heads" are considered metonymy, although using a part to represent the whole is more properly classified as synecdoche.
Metonymy comes from the Greek metonymia, meaning 'a change of name', constructed from the words meta-, meaning 'change', and onyma (from onoma) meaning 'name'.
Metonymy is pronounced meh-ton-uh-mee or mih-ton-uh-mee.