countersign vs watchword

countersign and watchword both are nouns.

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

As nouns, countersign and watchword are synonyms defined as:

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

Other synonyms of countersign include parole, password, word.

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

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