The term BE A CAST MEMBER OF can be solved by two five-letter words: ACTIN and APPIN. ACTIN is an abbreviation for the word 'acting, ' which is a form of performing in which an actor portrays a character in a play, movie, or television show. APPIN is an abbreviation for the word 'appearing, ' which is a form of performing in which an actor appears in a play, movie, or television show without having any lines. Both terms refer to being part of a cast in a production.