CAVE IN

{v.} 1. To fall or collapse inward. * /The mine caved in and crushed three miners./ * /Don't climb on that old roof. It might cave in./ 2. {informal} To weaken and be forced to give up. * /The children begged their father to take them to the circus until he caved in./ * /After the atomic bomb, Japan caved in and the war ceased./