Once

Once = (1) one time only: You have to take this medicine once a day. (2) whenever; as soon as: Once it stops raining, we can go out. (3) at some indefinite time in the past: She was a very popular actress once. (4) used in negative sentences and questions, and after if to mean ever or at all: He didn’t once thank me.If she once decides to do something, it becomes difficult to change her mind.