The term 'USED A MIRROR' can be summarized by the crossword solution 'PREENED, ' which is a 7-letter word. Preening is a behavior in which an animal, usually a bird, cleans and arranges its feathers with its beak. It is also used to describe humans grooming themselves, such as combing their hair or applying makeup. Therefore, the term 'USED A MIRROR' can be summarized as 'PREENED, ' which means to groom oneself using a mirror.