Synonyms/Hypernyms (Ordered by Estimated Frequency) of verb co-sign

2 senses of co-sign

Sense 1
co-sign, cosign -- (sign jointly; "Husband and wife co-signed the lease")
       => validate, formalize, formalise -- (declare or make legally valid)

Sense 2
cosign, co-sign -- (sign and endorse (another person's signature), as for a loan)
       => endorse, indorse -- (sign as evidence of legal transfer; "endorse cheques")