active has 7 distinct synonyms spread across 6 of its 17 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 6 recorded opposites are inactive, passive, quiet, stative, extinct, dormant.
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.
tending to become more severe or wider in scope
“active tuberculosis”
disposed to take action or effectuate change
“a director who takes an active interest in corporate operations”
characterized by energetic activity
“an active toddler”
exerting influence or producing a change or effect
“an active ingredient”
full of activity or engaged in continuous activity
“an active seaport”
(of the sun) characterized by an increased occurrence of sunspots and flares and radio emissions
expressing that the subject of the sentence has the semantic function of actor: "Hemingway favors active constructions"
(of e.g. volcanos) capable of erupting
(of e.g. volcanos) erupting or liable to erupt
“active volcanos”
the voice used to indicate that the grammatical subject of the verb is performing the action or causing the happening denoted by the verb
“`The boy threw the ball' uses the active voice”
a person who is a participating member of an organization
“the club issues a list of members, both the actives and the retirees”
Synonyms, antonyms and the broader and narrower relations for active come from Princeton University’s WordNet. Full sources and licences.