Main entry: retroactive
Definition: descriptive of any event or stimulus or process that has an effect on the effects of events or stimuli or process that occurred previously
Antonyms: proactive
Definition: descriptive of any event or stimulus or process that has an effect on events or stimuli or processes that occur subsequently
Main entry: retro, retroactive, ex post facto
Definition: affecting things past
Usage: retroactive tax increase; an ex-post-facto law; retro pay
Antonyms: prospective
Definition: of or concerned with or related to the future