action has 17 distinct synonyms spread across 7 of its 12 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 inaction.
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.
something done (usually as opposed to something said)
“there were stories of murders and other unnatural actions”
a process existing in or produced by nature (rather than by the intent of human beings)
“the action of natural forces”
the series of events that form a plot
“his novels always have a lot of action”
the trait of being active and energetic and forceful
“a man of action”
the operating part that transmits power to a mechanism
“the piano had a very stiff action”
a judicial proceeding brought by one party against another; one party prosecutes another for a wrong done or for protection of a right or for prevention of a wrong
an act by a government body or supranational organization
“recent federal action undermined the segregationist position”
the most important or interesting work or activity in a specific area or field
“the action is no longer in technology stocks but in municipal bonds”
put in effect
“carry out a task”
Synonyms, antonyms and the broader and narrower relations for action come from Princeton University’s WordNet. Full sources and licences.