watchword vs countersign

watchword and countersign both are nouns.

Word	Noun	Adjective	Verb	Adverb
watchword	Yes	No	No	No
countersign	Yes	No	Yes	No

As nouns, watchword and countersign are synonyms defined as:

watchword and countersign: a secret word or phrase known only to a restricted group

Other synonyms of watchword include parole, password, word.

watchword (noun)	countersign (noun)
a secret word or phrase known only to a restricted group	a second confirming signature endorsing a document already signed
a slogan used to rally support for a cause	a secret word or phrase known only to a restricted group

watchword (verb)	countersign (verb)
	add one's signature to after another's to attest authenticity