complex has 4 distinct synonyms spread across 4 of its 6 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is simple.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a compound described in terms of the central atom to which other atoms are bound or coordinated
Synonyms, antonyms and the broader and narrower relations for complex come from Princeton University’s WordNet. Full sources and licences.
(psychoanalysis) a combination of emotions and impulses that have been rejected from awareness but still influence a person's behavior
a whole structure (as a building) made up of interconnected or related structures
complicated in structure; consisting of interconnected parts
“a complex set of variations based on a simple folk melody”