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
(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”
Synonyms, antonyms and the broader and narrower relations for complex come from Princeton University’s WordNet. Full sources and licences.