A person or organization that shares sponsorship of an event, activity, or legislation with another sponsor.
From co- + sponsor (from Medieval Latin sponsor, 'one who pledges'). A modern term created to describe shared sponsorship arrangements.
In Congress, cosponsors of bills are actually a huge deal—when a senator cosponsors a bill, it signals their support and helps build momentum, which is why legislators compete to be early cosponsors.
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