GO BACK ON

{v. phr.} 1. To turn against; not be faithful or loyal to. * /Many of the man's friends went back on him when he was sent to prison./ * /The boy's father told him not to go back on his promise./ Compare: BACK DOWN, TURN ONE'S BACK. 2. To fail to do necessary work; not work. * /Grandfather's eyes are going back on him./ Compare: BREAK DOWN(4), GIVE OUT.