annul vs countermand

annul is not a noun while countermand is a noun.

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

As verbs, annul and countermand are synonyms defined as:

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

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

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