The term 'CRACKS UP' can be broken down into four crossword solutions: SLAYS (5 letters), AMUSES (6 letters), GOESMAD (7 letters), and GOESTOPIECES (12 letters). The term 'cracks up' is an idiom that means to make someone laugh or to amuse them. Therefore, the solution SLAYS could mean to make someone laugh so hard they are in tears, AMUSES could mean to make someone smile or chuckle, GOESMAD could mean to make someone laugh uncontrollably, and GOESTOPIECES could mean to make someone laugh hysterically.