Neptune

From Middle English Neptune, Neptunus, a borrowing from Latin Neptūnus, possibly from Proto-Indo-European *nébʰ-tu-s (“damp, cloudy”) (source of Ancient Greek νέφος (néphos), Sanskrit नभस् (nábhas), etc.), with the sense of "wet, moist." Puhvel, however, connects it with Proto-Italic *nepōts from Proto-Indo-European *népōts by analogy to Portūnus, cognate with Vedic Apām Napāt and Avestan Apąm Napāt, Child (cf: neve, nephew) of the Water as part of an Indo-European 'Fire in the Water' myth.

• (UK) IPA^(key): /ˈnɛptjuːn/, /ˈnɛptʃuːn/
• (US) IPA^(key): /ˈnɛptuːn/
• (New Zealand) IPA^(key): /ˈneptʃʉːn/
• enPR: nĕp′to͞on′, nĕp′tyo͞on′

• Audio (US):

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• Hyphenation: Nep‧tune

Neptune

2. (astronomy) The eighth planet in our solar system, represented in astronomy and astrology by ♆. [from 1846]
   • 1846 November 21, “A NEW PLANET-BEAUTIFUL DISCOVERY.”, in Chambers's Edinburgh Journal, number 146, page 336, column 1:

     At a meeting of the French Academy of Science, M. Leverrier presented a fifth and final memoir on the new planet, which M. Arago proposes to be called Neptune.

   • 1897, H. G. Wells, The Star‎^[1] (Science Fiction):

     It was on the first day of the new year that the announcement was made, almost simultaneously from three observatories, that the motion of the planet Neptune, the outermost of all the planets that wheel about the sun, had become very erratic. Ogilvy had already called attention to a suspected retardation in its velocity in December. Such a piece of news was scarcely calculated to interest a world the greater portion of whose inhabitants were unaware of the existence of the planet Neptune, nor outside the astronomical profession did the subsequent discovery of a faint remote speck of light in the region of the perturbed planet cause any very great excitement. Scientific people, however, found the intelligence remarkable enough, even before it became known that the new body was rapidly growing larger and brighter, that its motion was quite different from the orderly progress of the planets, and that the deflection of Neptune and its satellite was becoming now of an unprecedented kind.

   • 2024 June 27, Zulfikar Abbany, “Asteroids and comets: What's the difference?”, in Deutsche Welle‎^[2], archived from the original on 11 January 2026:

     The duration of planetary orbits ranges widely. Mercury — the closest planet to the sun — has an 88-day orbit, while Earth, the third from the sun, takes 365 days (1 year).
     Mars needs almost twice that time to fly around the sun, while Saturn takes 10,759 days (29.4 years). Neptune, the furthest planet from the sun, has an orbit of 60,190 days (164.9 years).

4. (Roman mythology) The god of the ocean and of earthquakes, equivalent to Poseidon in Greek mythology.

   Alternative form: Neptunus

   • 1595, The Lives of the Noble Grecians and Romanes, Compared together by that Grave Learned Philosopher and Historiographer, Plutarke of Chæronea‎^[3], translation of original in Ancient Greek, page 3:

     And Pitheus alſo had giuen it out abroad, that he was begotten of Neptune, becauſe the TROEZENIANS haue this god in great veneration, and doe worſhip him as patron and protector of their citie, making offerings to him of their firſt fruits: and they haue for the marke and ſtamp of their money, the three picked mace, which is the ſigne of Neptune, called his Trident.

5. A township in Monmouth County, New Jersey, United States.
6. An unincorporated community in Mercer County, Ohio.
8. An unincorporated community in Jackson County, West Virginia.
10. An unincorporated community in Ithaca, Richland County, Wisconsin.

• (astronomy, astrology): ♆
• (astronomy): (rare) ⯉

• planets of the Solar System: Mercury · Venus · Earth · Mars · Jupiter · Saturn · Uranus · Neptune ^[edit]
• Poseidon

From Latin Neptūnus.

• IPA^(key): /nɛp.tyn/

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• Audio (Switzerland (Valais)):

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Neptune m

2. Neptune (planet)
4. (Roman mythology) Neptune (Roman god of the sea)