[ nep-toon, -tyoon ]

  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.

Origin of neptune

<New Latin Neptunea;see Neptune, -ea

Words Nearby neptune

Other definitions for Neptune (2 of 2)

[ nep-toon, -tyoon ]

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

  2. the sea or ocean: Neptune's mighty roar.

  1. 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.

  2. a township in E New Jersey. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use neptune in a sentence

  • Reckoning that neptune is the outermost planet of the solar system, that system would have a diameter of 5,584 millions of miles.

    God and my Neighbour | Robert Blatchford
  • The captain immediately went on deck, and neptune hailed from the fore part of the rigging, "What ship?"

  • Strange to say, the dog neptune was the only one on board that appeared to mourn the loss of this passenger.

  • Tell mother not to be uneasy on that point, for though neptune has the heart of a lion he has the temper of a lamb.

  • Our main radio is dead without fuel to run its dynamotors, and our auxiliary set hasn't the power to reach neptune.

    The Sargasso of Space | Edmond Hamilton

British Dictionary definitions for Neptune (1 of 2)


/ (ˈnɛptjuːn) /

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

British Dictionary definitions for Neptune (2 of 2)


/ (ˈnɛptjuːn) /

  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

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

Scientific definitions for Neptune


[ nĕptōōn′ ]

  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. See Table at solar system.

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Cultural definitions for Neptune (1 of 2)


The Roman and Greek god who ruled the sea.

Notes for Neptune

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

Notes for Neptune

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

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.”)

Notes for Neptune

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.

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.