combine has 17 distinct synonyms spread across 7 of its 10 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. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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.
add together from different sources
“combine resources”
harvester that heads and threshes and cleans grain while moving across the field
a consortium of independent organizations formed to limit competition by controlling the production and distribution of a product or service
“they set up the trust in the hope of gaining a monopoly”
Synonyms, antonyms and the broader and narrower relations for combine come from Princeton University’s WordNet. Full sources and licences.