synchronise has 4 distinct synonyms spread across 6 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 desynchronise.
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.
make (motion picture sound) exactly simultaneous with the action
“synchronize this film”
cause to indicate the same time or rate
“synchronize your watches”
make synchronous and adjust in time or manner
“Let's synchronize our efforts”
Synonyms, antonyms and the broader and narrower relations for synchronise come from Princeton University’s WordNet. Full sources and licences.