From Miriam Webster thesaurus:
component
noun
Synonyms and Antonyms of COMPONENT
one of the parts that make up a whole <each set is composed of several distinct components
Synonyms building block, component, constituent, factor, ingredient, member
Related Words basis, part and parcel; detail, item, particular, point; aspect, characteristic, facet, feature, trait; division, fragment, particle, partition, piece, portion, section, sector, segment; subcomponent
Near Antonyms aggregate, composite, compound, mass; entirety, sum, summation, total, totality; admixture, amalgam, amalgamation, blend, combination, intermixture, mix, mixture
Antonyms whole
I actually love the meaning of constituent (1. any one of the people who live and vote in an area : a member of a constituency, 2. one of the parts that form something) but of course it’s too long 
There were some others I liked too but let’s open it up (and not be restricted to synonyms).