Metonymy

Noun
Rhetoric
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 “count people.”
dictionary.com

My colleague and I discovered this word today and I think it makes for a wonderful word of the day.