co·spon·sor (kō-spŏn'sər) tr.v.
co·spon·sored, co·spon·sor·ing, co·spon·sors To function in the capacity of a joint sponsor of: corporations that cosponsored a marathon. n. A joint sponsor: two senators who were cosponsors of new legislation. co·spon'sor·ship' n.