C / con-sponsor
noun

con-sponsor

gen. con-sponsōris · gender masculine · decl. 3rd
A joint surety
A joint surety, Cic. Fam. 6, 18, 2; id. Att. 12, 17.—
One who binds; obligates himself to something
One who binds or obligates himself to something ( = conjurator), acc. to Fest. p. 59, 7 Müll.