countermand vs annul

countermand is a noun but annul is not a noun.

Word	Noun	Adjective	Verb	Adverb
countermand	Yes	No	Yes	No
annul	No	No	Yes	No

As verbs, countermand and annul are synonyms defined as:

Other synonyms of countermand include lift, overturn, repeal, rescind, reverse, revoke, vacate.

countermand (noun)	annul (noun)
a contrary command cancelling or reversing a previous command

countermand (verb)	annul (verb)
cancel officially	cancel officially
	declare invalid