co-sign
1. [ verb ] (law) sign jointly
Synonyms: cosign
Examples:

"Husband and wife co-signed the lease"

Related terms: validate cosignatory
2. [ verb ] sign and endorse (another person's signature), as for a loan
Synonyms: cosign
Related terms: endorse cosigner
Similar spelling:   cosign
  cosigner
  cockaigne
  coseismic
  coseismal
  cosecant