The term 'past its prime' is used to describe something that is no longer in its best condition. This could refer to a person, object, or idea. The crossword solutions for this term are OLD (3 letters), STALE (5 letters), and WORN (4 letters). These words all imply that something has been around for a long time and is no longer as fresh or new as it once was. OLD implies that something has been around for a long time and is no longer as effective or desirable as it once was. STALE implies that something has lost its flavor or appeal over time. WORN implies that something has been used for a long time and is no longer in good condition. All of these words together suggest that something has gone beyond its peak and is no longer at its best.