The term 'REALLY, REALLY GOOD' can be summarized by two crossword solutions: STELLAR (7 letters) and FIRSTRATE (9 letters). STELLAR is an adjective meaning of or relating to the stars, or exceptionally good or impressive. It is derived from the Latin word for star, 'stella'. FIRSTRATE is an adjective meaning of the highest quality or standard. It is derived from the phrase 'first rate', which has been used since the 16th century to describe something of the highest quality. Together, these two words provide a succinct summary of the term 'REALLY, REALLY GOOD'.