The term 'GREAT SERVE' can be broken down into two crossword solutions: ACE (3 letters) and POINTOFNORETURN (15 letters). ACE is a term used in tennis to describe a serve that is so powerful and accurate that the opponent cannot return it. Point of No Return is a phrase used to describe a situation in which a decision has been made and there is no turning back. Together, these two terms can be used to describe an exceptional serve in tennis that is so powerful and accurate that the opponent cannot return it, thus making it a point of no return.