from dictionary.com
me·ton·y·my /mɪˈtɒnəmi/ Show Spelled
[mi-ton-uh-mee] Show IPA
–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.”
The definition of meronym shown in my previous post actually uses the words in the clue so I'm going with meronym