surgical operation has 4 distinct synonyms spread across 1 of its 1 sense. 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.
a medical procedure involving an incision with instruments; performed to repair damage or arrest disease in a living body
“they will schedule the operation as soon as an operating room is available”
Synonyms, antonyms and the broader and narrower relations for surgical operation come from Princeton University’s WordNet. Full sources and licences.