validate vs co-sign

validate and co-sign both are verbs.

Word	Noun	Adjective	Verb	Adverb
validate	No	No	Yes	No
co-sign	No	No	Yes	No

As verbs, co-sign is a hyponym of validate; that is, co-sign is a word with a more specific, narrower meaning than validate:

Other hyponyms of validate include ratify, sign, cosign, probate.

validate (verb)	co-sign (verb)
make valid or confirm the validity of	sign and endorse (another person's signature), as for a loan
prove valid; show or confirm the validity of something	sign jointly
give evidence for
declare or make legally valid