cosign UK /ˈkəʊ.saɪn/US /ˈkoʊ.saɪn/verb 2noun 1forms 3 verb2 •To sign a document jointly with another person, sometimes as an endorsement. •(informal) To agree with or endorse. noun1 •The promotion of one musical artist (usually less successful) by another.Also, you can't base your entire career on cosigns and big features. At some point, your music has to stand on its own. — 2013 formscosigned · cosigning · cosigns