meronym

noun

1. A term used to denote a thing that is a part of something else.

   “The word "leaf" is a meronym of the word "tree".”

   “If one starts with some complex whole, like {automobile} or {human_body}, it can be broken down into several levels of meronyms, but many of those meronyms will also be meronyms of other wholes. That is to say, some components serve as parts of many different things: think of all the different mechanisms that have gears.”