Available Definitions:
1) 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.
2) v. t. - To prohibit; to forbid.
3) v. t. - To oppose; to revoke the command of.
4) n. - A contrary order; revocation of a former order or command.