synchronic has 2 distinct synonyms spread across 1 of its 3 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 diachronic.
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.
occurring or existing at the same time or having the same period or phase
“recovery was synchronous with therapy”
concerned with phenomena (especially language) at a particular period without considering historical antecedents
“synchronic linguistics”
1 of the 3 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for synchronic.
Synonyms, antonyms and the broader and narrower relations for synchronic come from Princeton University’s WordNet. Full sources and licences.