The crossword solution for the term 'IS ON FIRST' is 'OPENS, ' which is a five-letter word. This phrase is a reference to the classic Abbott and Costello comedy routine, 'Who's on First?' In the routine, Abbott and Costello have a conversation about the names of baseball players, with Abbott trying to explain that the player named 'Who' is on first base. The word 'opens' is used in the routine to describe the action of the player on first base.