cosmonaut UK /ˈkɒz.məˌnɔːt/US /ˈkɑz.məˌnɔt/ noun1 •An astronaut, especially a Russian or Soviet one.Khrushchev’s answer came 60 years ago, on April 12, 1961, when Soviet cosmonaut Yuri Gagarin circled the Earth aboard a spacecraft called Vostok 1. — 2021 formscosmonauts