The OED says -naut forms words with the sense of voyager or traveller. Here are some more examples:
- aeronaut – a balloonist; a spider which floats through the air
- aquanaut – an underwater explorer
- Argonaut – one of the legendary heroes who sailed with Jason in the Argo
- cosmonaut – a Soviet or Russian astronaut
- psychonaut – someone who experiments with psychedelic drugs
- Reaganaut – an advocate of the policies of US President Reagan
The word juggernaut (a heavy lorry) has quite a different etymology.