The term 'run its course' is an idiom that means to come to a natural END. It is often used to describe situations where something has been allowed to progress naturally without interference, and eventually comes to an END. The two crossword solutions for this term are 'ELAPSE' (6 letters) and 'END' (3 letters). ELAPSE means to pass or go by gradually, while END means the conclusion or termination of something. Therefore, both words can be used to describe the idiom 'run its course, ' as they both refer to the idea of something coming to a natural conclusion.