The combining form -naut gives English several words that convey a type of traveler.
The Greek word for sailor was ναύτης (nautes). Classical Latin mesonauta referred to a sailor “intermediate in rank between a rower and a steersman.” Classical Latin Argonauta referred to the sailors who traveled with Jason in the Argo (his ship).
The earliest “naut word” in English is the noun Argonaut (1596): one of the legendary heroes who accompanied Jason in the Argo in his quest of the Golden Fleece. Because of their quest for gold, the US “forty-niners” (gold-seekers who went to California in 1849) were also referred to as argonauts.
Here, with the date of their earliest citation in the OED, are some other “naut words” in English:
A person who makes balloon ascents or flies in a balloon, a balloonist.
An underwater ‘explorer’ or swimmer.
A person who travels in space; especially a person who is (or has been) a crewmember on board a spacecraft or on a space mission.
A traveler in outer space; an astronaut (especially a Russian space traveler).
(1965) A robot
(1973) A computer user
(1990) A person who interacts with a virtual reality environment using computer technology
A user of the Internet, especially a skilled or habitual one.
Note: Internaut first shows on the Ngram Viewer in 1991 and leaps upward from there. In French, the word internaute is the equivalent of “internet user.” According to Wikipedia, English internaut “refers to operators or technically highly capable users of the Internet,” but internaut as a one-word option for “internet user” has its appeal.
oceanaut (1962) Another word for aquanaut.
If you are wondering why juggernaut is not in the list of “naut words,” here’s your answer.
The naut in juggernaut is not the combining form that means sailor or traveler. It’s an accident of spelling. In Hindu religion, Jaggernaut is a title of Krishna. The title derives from Hindi Jagannath, “Lord of the world.”
In an annual ceremony, a representation of this incarnation is carried in procession by an enormous vehicle. The ritual is especially associated with the town of Puri in India. According to legend, devotees there once allowed themselves to be crushed under the wheels of the cart in sacrifice.
The word juggernaut is used figuratively to mean, “anything that demands blind devotion or merciless sacrifice” and “a massive inexorable force or object that advances irresistibly and crushes whatever is in its path.” For example,
Donald Trump is a political juggernaut with a carnival barker’s draw.—Dallas News
Game of Thrones: Can HBO’s Juggernaut Maintain Its Momentum?—The Fiscal Times.
In the following examples, the word unstoppable is redundant:
The big unstoppable juggernaut proved the inspiration for so many players—Independent (Ireland)
At first glance the Argonaut High girls basketball team looks like an unstoppable juggernaut. Auburn Journal