(1):

(n.) A contrary order; revocation of a former order or command.

(2):

(v. t.) To prohibit; to forbid.

(3):

(v. t.) To revoke (a former command); to cancel or rescind by giving an order contrary to one previously given; as, to countermand an order for goods.

(4):

(v. t.) To oppose; to revoke the command of.