- Neptune
- c.1385, from L. Neptunus, the Roman god of the sea (later identified with Gk. Poseidon), probably from PIE base *(e)nebh- "moist" (cf. L. nebula "fog, mist, cloud;" see nebula). The planet so named was discovered by Galle in 1846. Until the identification of Pluto in 1930, it was the most distant planet known. Neptunian (1794) in the geological sense refers to actions of water; usually opposed to volcanic or plutonic.
- plutonium
- 1942, from Pluto, the planet (see Pluto), the element named on suggestion of Seaborg and Wahl because it follows neptunium in the periodic table as Pluto follows Neptune in the Solar System.
- Pluto
- Roman god of the underworld, brother of Zeus and Neptune, from L. Pluto, from Gk. Plouton "god of wealth," lit. "wealth, riches," probably originally "overflowing," from PIE *pleu- "to flow. The planet (since downgraded) was discovered 1930 by C.W. Tombaugh; Minerva also was suggested as a name for it. The cartoon dog first appeared in Walt Disney's "Moose Hunt," released April 1931.