crack up

v.

1. *To crash a vehicle

   collide, be in an accident, smash up, total*; see crash 4.

2. To fail suddenly in health, mind, or strength

   go to pieces, decline, fail, deteriorate, sicken, collapse, succumb, break down, go crazy, go mad, become insane, have a nervous breakdown, become psychotic, be committed to a hospital, be committed to an institution, fall apart, burn out, crack, flip out*, flip one's lid*, freak out*, go out of one's mind*, blow one's mind*, go off one's rocker*, go off the deep end*, come apart at the seams*, lose it*; see also derange 2, weaken 1.

3. *To laugh

   roar, howl, burst out laughing, roll in the aisles*; see laugh.