An act of war is a hostile action taken by one nation against another. It can involve physical force, such as military attacks, or economic pressure, such as sanctions. The two crossword solutions for the term 'act of war' are 'TUG' and 'SIEGE'. A TUG is a type of boat used to pull or push larger vessels, and it is often used in naval warfare. A SIEGE is a prolonged military operation in which an attacking force surrounds a defended location in order to weaken its defenses and force surrender.