operational has 6 distinct synonyms spread across 2 of its 4 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 nonoperational.
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.
fit or ready for use or service
“the toaster was still functional even after being dropped”
(military) of or intended for or involved in military operations
being in effect or operation
“de facto apartheid is still operational even in the `new' African nations”
1 of the 4 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 operational.
Synonyms, antonyms and the broader and narrower relations for operational come from Princeton University’s WordNet. Full sources and licences.