trimerous
Organized in threes; having parts in numbers that are multiples of three.
The monocots typically have trimerous flowers.
Having three joints.
Where it comes from
From tri- + -merous; ultimately from tri-, from Ancient Greek τρία (tría, “three”); + Ancient Greek μέρος (méros, “part”).
Adapted from the Wiktionary entry trimerous (CC BY-SA 4.0).