[ nep-too-nee-uh n, -tyoo- ]
/ nɛpˈtu ni ən, -ˈtyu- /


pertaining to Neptune or the sea.
pertaining to the planet Neptune.
(often lowercase) Geology. formed by the action of water.

Origin of Neptunian

First recorded in 1650–60; Neptune + -ian

Related forms

trans-Nep·tu·ni·an, adjective Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for neptunian

British Dictionary definitions for neptunian


/ (nɛpˈtjuːnɪən) /


of or relating to the Roman god Neptune or the sea
of, occurring on, or relating to the planet Neptune
geology (of sedimentary rock formations such as dykes) formed under water
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012