If you countermand an order, you cancel it, usually by giving a different order. I can't countermand an order Winger's given. = override, overrule. to officially tell people to ignore an order, especially by giving them a different one (contremander, from contre- ( COUNTER-) + mander (from mandare))
[ 'kaun-t&r-"mand, "kaun-t&a ] (transitive verb.) 15th century. From Old French contremander, from mediaeval Latin contramandare, from contra- + mandare ‘command’.