1550s, "pertaining to the planet Saturn;" 1610s, "pertaining to the god Saturn or his reign," from French saturnien, from Latin saturnius, from Saturn (see Saturn).
As a noun, 1590s as "one born under the influence of Saturn;" by 1738 as "a native or inhabitant of Saturn."
Some cold Saturnian, when the lifted tube
Shows to his wond'ring eye our pensile globe,
Pities our thirsty soil, and sultry air,
And thanks the friendly pow'r that fix'd him there.
[Richard Savage, "The Genius of Liberty," dated 1734, published in Gentleman's Magazine, June 1738]
updated on December 31, 2021