The crossword solution for the term USE, AS A KEY is TURN. The term 'TURN' can be used to describe a variety of actions. It can refer to the act of rotating or spinning around an axis, such as when turning a key in a lock. It can also refer to changing direction, such as when turning a corner or turning a page in a book. Additionally, it can refer to changing one's opinion or attitude, such as when someone turns away from a bad habit. Finally, it can refer to the act of transforming something, such as when a caterpillar turns into a butterfly.