from The American Heritage® Dictionary of the English Language, 4th Edition
- transitive v. To sign (a document) jointly.
- transitive v. To endorse (another's signature), as for a loan.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- v. To sign a document jointly with another person, sometimes as an endorsement.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- v. sign jointly
- v. sign and endorse (another person's signature), as for a loan
co- + sign (Wiktionary)