Neptunian (adj.)youdaoicibaDictYouDict[Neptunian 词源字典]
1650s as "pertaining to the god Neptune;" 1794 in the geological sense, referring to actions of water, from Neptune + -ian. Usually opposed to volcanic or plutonic. As a noun meaning "inhabitant of the planet Neptune" it is recorded from 1870.[Neptunian etymology, Neptunian origin, 英语词源]