— used to talk about something that might happen or be true but that is not likely对…抱有一丝希望；碰碰运气
I called his office on the off chance that he would still be there [=I called because I thought there was a slight chance that he would still be there], but he had already left.我往他的办公室打电话，只是碰碰运气希望他还在，但他已经离开了。