The term 'Act on a ___' can be completed with two different words: 'DEED' and 'HUNCH'. A DEED is an action or legal document that serves as evidence of a right or agreement. A HUNCH is an intuitive feeling or guess about something, often without any evidence to support it. Acting on a DEED would involve taking some kind of action based on a legal document, while acting on a HUNCH would involve making a decision based on intuition.