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• neptune
  neptune

  noun

  any whelk of the genus Neptunea, especially N. decemcostata, common along the eastern coast of North America and having a shell with seven to ten raised reddish-brown spiral ridges on a pale beige or yellow background.
• Neptune
  Neptune

  noun

  the ancient Roman god of the sea, identified with the Greek god Poseidon.

neptune

¹ American  

[nep-toon, -tyoon] / ˈnɛp tun, -tyun /

noun

1. any whelk of the genus Neptunea, especially N. decemcostata, common along the eastern coast of North America and having a shell with seven to ten raised reddish-brown spiral ridges on a pale beige or yellow background.

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Neptune ² American  

[nep-toon, -tyoon] / ˈnɛp tun, -tyun /

noun

1. the ancient Roman god of the sea, identified with the Greek god Poseidon.

2. the sea or ocean.

   Neptune's mighty roar.

3. Astronomy. the planet eighth in order from the sun, having an equatorial diameter of 30,200 miles (48,600 km), a mean distance from the sun of 2794.4 million miles (4497.1 million km), a period of revolution of 164.81 years, and two moons.

4. a township in E New Jersey.

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Neptune ¹ British  

/ ˈnɛptjuːn /

noun

1. Greek counterpart: Poseidon.  the Roman god of the sea

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Neptune ² British  

/ ˈnɛptjuːn /

noun

1. the eighth planet from the sun, having fourteen known satellites, the largest being Triton and Nereid, and a faint planar system of rings or ring fragments. Mean distance from sun: 4497 million km; period of revolution around sun: 164.8 years; period of rotation: 14 to 16 hours; diameter and mass: 4.0 and 17.2 times that of earth respectively

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Neptune Scientific  

/ nĕp′to̅o̅n′ /

1. The eighth planet from the Sun and the fourth largest, with a diameter almost four times that of Earth. Neptune is a gas giant with a very active weather system, exhibiting extremely long and powerful storms with the fastest winds observed in the solar system. Neptune's axis is tilted 28.8° from the plane of its orbit, and its summer and winter seasons each last 40 years. For a period of 20 years out of every 248, Pluto's highly elliptical orbit crosses within that of Neptune. Neptune has four faint rings and 13 known moons and appears blue due to the absorption of red light by the methane within its atmosphere.

2. See Table at solar system

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Neptune ¹ Cultural  

1. The Roman and Greek god who ruled the sea.

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Neptune ² Cultural  

1. In astronomy, a major planet, the eighth planet from the sun. Neptune is named for the Roman god of the sea. Neptune is similar in size and composition to Uranus. It is usually visible only through a telescope and was discovered in the 1840s. For a period ending in 1999, Pluto's orbit took it inside the orbit of neptune. (See solar system; see under “Mythology and Folklore.”)

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Discover More

The eighth planet from the sun (the Earth is third) is named Neptune.

Neptune is frequently portrayed as a bearded giant with a fish's scaly tail, holding a large three-pronged spear, or trident.

Some astronomers have suggested that Pluto is not a planet in the usual sense but is an object more like an asteroid, and that Neptune, therefore, is actually the outermost planet.

Etymology

Origin of neptune

< New Latin Neptunea; see Neptune, -ea

Example Sentences

The deep interiors of ice giant planets such as Uranus and Neptune may contain a previously unknown form of matter.

From Science Daily • Apr. 21, 2026

Just after sunset, Mercury, Venus, Saturn, and Neptune will appear low in the western sky, close to the horizon.

From BBC • Feb. 27, 2026

After loading up oil at Venezuela’s Jose Terminal in November, the Skipper offloaded oil to the Neptune 6, on Dec. 6, according to Kpler.

From The Wall Street Journal • Feb. 22, 2026

The innermost world is rocky, followed by two gas rich planets similar to smaller versions of Neptune, a lineup that matches standard expectations.

From Science Daily • Feb. 14, 2026

“Cyclopes! I tell you, Stheno, when I destroy Neptune and take over the oceans, we will renegotiate the Cyclopes’ labor contract.

From "The Son of Neptune" by Rick Riordan

Related Words

• earth