astronaut (or cosmonaut) is a person specially trained to serve aboard a spacecraft. The term was generally used in the 20th and 21st centuries, at a time when space flight was rare and particularly risky.
Nyota Uhura used the word "astronauts" to refer to the crew of the USS in one of her songs. ( Enterprise TOS episode: " Charlie X")
Anne Gauvreau referred to the Talin who embarked on a mission to their planet's moon circa the 2270s as astronauts, though Pavel Chekov insisted "cosmonaut" was the correct term. ( TOS novel: )
After some convincing,
Zefram Cochrane finally came to accept that the crew of the USS were astronauts, of a sort. ( Enterprise-E TNG movie & novelization: )
Star Trek: First Contact Benjamin Sisko had read about astronauts who used one of their thumbs to obscure the Earth from their view. ( DS9 novel: )
Julian Bashir had seen images of Russian cosmonauts who had to be carried out of their craft by stretcher after returning to Earth. ( - DS9 Mission Gamma novel: )