Neptunian UK /nɛpˈtjuː.nɪ.ən/US /nɛpˈt(j)u.ni.ən/adjective 6noun 4forms 2 adjective6 •Of or pertaining to Neptune, the Roman god of fresh water and the sea, the counterpart of the Greek god Poseidon. •Pertaining to the astrological influence of the planet Neptune. •Of or pertaining to the planet Neptune.Neptune has a faint ring system and 14 known moons. The largest of these is Triton, which contains over 90% of the mass of all the Neptunian moons, and is the only Neptunian moon that's spherical. — 2017 •Formed by the action of water. •(historical) Of, pertaining to, or supporting Neptunism (“a discredited theory that rocks were formed from the crystallisation of minerals in the early Earth's oceans”). •(rare) Of or pertaining to water or the sea. noun4 •An (imaginary) inhabitant of the planet Neptune. •A person under the astrological influence of the planet Neptune.To a Neptunian the common satisfaction of life seems too banal, and he often seeks the hidden mysteries of life. The advanced soul however realises that life is a dream, and a divine dream at that. — 1983 •(historical) A proponent of Neptunism.Its [obsidian's] origin is warmly contested between the Neptunians and Plutonians, many of the latter denominating it a vitreous lava. — 1813 •(no longer used) A sailor.You braue Neptunians, you salt water crew, / Sea-plowing Marriners; I speake to you: [...] — 1620 formsNeptunians · neptunians