1. Descriptive of any event or stimulus or process that has an effect on events or stimuli or processes that occur subsequently
   "proactive inhibition"; "proactive interference" 
2. (of a policy or person or action) controlling a situation by causing something to happen rather than waiting to respond to it after it happens

See also: active

Antonym: retroactive

Encyclopedia: Proactive Proactive, Preemptive Operations Group

• output file
• output program
• output routine
• output signal
• output-to-input ratio
• outrace
• outrage
• outraged
• outrageous
• outrageously
• outrageousness
• outrange
• outrank
• outreach
• outride
• outrider
• outrigged
• outrigger
• outrigger canoe
• outright
• outrival
• outroar
• outrun
• outré
• outsail