meronym
A term used to denote a thing that is a part of something else.
The word "leaf" is a meronym of the word "tree".
Where it comes from
From mero- + -onym, from Ancient Greek μέρος (méros, “part”) + ὄνυμα (ónuma, “name”).
Adapted from the Wiktionary entry meronym (CC BY-SA 4.0).