activation has 2 distinct synonyms spread across 1 of its 3 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 2 recorded opposites are inactivation, deactivation.
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.
stimulation of activity in an organism or chemical
the activity of causing to have energy and be active
making active and effective (as a bomb)
Synonyms, antonyms and the broader and narrower relations for activation come from Princeton University’s WordNet. Full sources and licences.