Act on Definition 1 of 3Pro Tip 1/3Prompt Action 'Act on' implies immediate or swift action based on the received information. He acted on the evacuation alert instantly. Pro Tip 2/3Based on Instructions Use 'act on' when someone does something as a direct result of instructions given. She acted on her coach's strategy during the game. Pro Tip 3/3Trust Implied Using 'act on' suggests trust in the source of advice or information. The investor acted on the analyst's report.