Bust a gut is an idiom that means to LAUGH so hard that it causes physical pain. The crossword solutions for this term are CRACKUP (7 letters), ROAR (4 letters), LAUGH (5 letters), YUKITUP (7 letters), BEINSTITCHES (12 letters), LAUGHOUTLOUD (12 letters), ERUPTINLAUGHTER (15 letters), and ROLLINTHEAISLES (15 letters). All of these words describe different ways of laughing, from the light chuckle of 'crackup' to the loud guffaw of 'laughoutloud' and the uncontrollable laughter of 'eruptinlaughter'.