synthesize has 1 distinct synonym spread across 1 of its 2 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 analyze.
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.
combine so as to form a more complex, product
“his operas synthesize music and drama in perfect harmony”
combine and form a synthesis
“Vitamin D only synthesizes when sunlight is available”
Synonyms, antonyms and the broader and narrower relations for synthesize come from Princeton University’s WordNet. Full sources and licences.