acceleration 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 one recorded opposite is deceleration.
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.
an increase in rate of change
“modern science caused an acceleration of cultural change”
the act of accelerating; increasing the speed
(physics) a rate of increase of velocity
Synonyms, antonyms and the broader and narrower relations for acceleration come from Princeton University’s WordNet. Full sources and licences.