Astronaut refers to a person engaged in or trained for spaceflight. Cosmonaut is the term used for a Russian or Soviet astronaut. Cosmonaut is a borrowing of the Russian word kosmonávt. Cosmo- comes from the Greek root kosmos-, meaning “universe,” while astro- comes from the Greek root astra- meaning “star.”https://www.dictionary.com/compare-words/cosmonaut-vs-astronaut