to fail to keep a promise, or to change a decision or agreement违背(承诺或协议);改变(决定)
The government looks likely to go back on its decision to close the mines.看来政府可能会出尔反尔,推翻原先关闭矿井的决定。
She's gone back on her word and decided not to give me the job after all.她说话不算话,竟然决定不再给我那个工作了。