When an officer in the military shouts, “Belay that order, Private!” that is a countermand. A countermand is an order that cancels or reverses an earlier command. Countermand is also used as a verb meaning “to cancel or revoke.”
Counter means “opposing” or “opposite,” and mand is short for “mandate” or “command.” Put them together and you’ve got countermand — an “opposing command.” When you issue a countermand, you cancel the original command and usually replace it with a new one. Countermand is often used in a military context, but it can be applied more widely. If your parents tell you to take out the trash, you might countermand these orders by telling your little brother to do it instead.