functioning has 2 distinct synonyms spread across 1 of its 2 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 malfunctioning.
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.
process or manner of functioning or operating
“the power of its engine determines its operation”
performing or able to perform its regular function
“a functioning flashlight”
Synonyms, antonyms and the broader and narrower relations for functioning come from Princeton University’s WordNet. Full sources and licences.