Wiktionary
Usage examples of "cosponsors".
Corrigan was too preoccupied with technical issues to pay much attention to background politics, but one day the company announced that Feller & Faber were coming in as cosponsors of Oz, which would be set up and run under a new, jointly owned corporation, "Xylog," dedicated to the project.
If the United States cosponsors it in the Security Council, what option have you?