The term 'act upon' can be defined as taking action based on a certain INFLUENCE, obedience, or effect. The crossword solutions for this term are INFLUENCE (9 letters), OBEY (4 letters), and AFFECT (6 letters). INFLUENCE refers to the power to AFFECT someone or something, while OBEY means to comply with an order or rule. Lastly, AFFECT is used to describe the impact that something has on a person or thing. Therefore, when one acts upon something, they are taking action based on the INFLUENCE, obedience, or effect of that thing.