https://en.oxforddictionaries.com/definition/astronaut
https://en.oxforddictionaries.com/definition/cosmonaut
https://en.oxforddictionaries.com/definition/taikonaut
http://www.merriam-webster.com/dictionary/astronaut
http://www.merriam-webster.com/dictionary/cosmonaut
[ Merriam-Webster doesn't define Taïkonaut ]
I just wanted to highligth that only NASA (or English speaker world) call their astronaut "astronaut". In europe, we call them spationauts. And in russia, they call them "cosmonauts".
Also, nobody in Denmark says spationaut. We say Astronaut, so not all of Europe and not only English speakers.
But yeah, the american word it has probably won in the popular culture and in the day-to-day language.
Sorry. I didn't want to sound like Mr. know it all.