[ ploo-toh ]
/ ˈplu toʊ /
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Classical Mythology. a name given to Hades, under which he is identified by the Romans with Orcus.
Astronomy. a dwarf planet having an equatorial diameter of about 2,100 miles (3,300 km), a mean distance from the sun of 3.674 billion miles (5.914 billion km), a period of revolution of 248.53 years, and one known moon, Charon. Based on the definition of a planet devised by the International Astronomical Union in 2006, Pluto, regarded as the ninth and most distant planet in our solar system since its discovery in 1930, was reclassified as a dwarf planet, a decision that continues to be examined and questioned by some astronomers.
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How to use Pluto in a sentence

British Dictionary definitions for Pluto (1 of 3)

/ (ˈpluːtəʊ) /

classical myth the god of the underworld; Hades

British Dictionary definitions for Pluto (2 of 3)

/ (ˈpluːtəʊ) /

the second-largest dwarf planet in the solar system, located in the Kuiper belt; discovered in 1930 by Clyde Tombaugh (1906–97); classified as a planet until 2006, when it was reclassified as a dwarf planet. It has a diameter of 2390 km

Word Origin for Pluto

Latin, from Greek Ploutōn, literally: the rich one

British Dictionary definitions for Pluto (3 of 3)

/ (ˈpluːtəʊ) /

the code name of pipelines laid under the English Channel to supply fuel to the Allied forces landing in Normandy in 1944

Word Origin for PLUTO

C20: from p (ipe) l (ine) u (nder) t (he) o (cean)
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 Pluto

[ plōōtō ]

A dwarf planet that until 2006 was classified as the ninth planet in the Solar System. Pluto was not discovered until 1930, when Clyde Tombaugh noticed it while searching for an unknown planet thought to influence Uranus's orbit. Pluto's surface is covered with frozen methane and other ices, and its extremely thin atmosphere consists primarily of methane and nitrogen. Between 1979 and 1999 Pluto crossed inside Neptune's orbit. Pluto has three moons: Charon (discovered in 1978) and Hydra and Nix (both discovered in 2005). 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 Pluto (1 of 2)


The Roman name of Hades, the Greek and Roman god of the underworld and ruler of the dead.

notes for Pluto

The planet Pluto is usually the most distant planet in the solar system.

Cultural definitions for Pluto (2 of 2)


In astronomy, the smallest of the major planets, usually ninth from the sun. Pluto was discovered in 1930 and is named for the Roman god of the underworld. (See solar system)

notes for Pluto

Astronomers in the late nineteenth century, thinking they saw disturbances in the orbits of Uranus and Neptune, suspected that there was a ninth planet, not yet discovered, exerting gravitation on the other two. In the early twentieth century, astronomers searched for that planet and found Pluto. Ironically, Pluto is much too small to be the planet they sought.

notes for Pluto

Pluto's orbit is a stretched ellipse, unlike the orbits of the other major planets, which are nearly circular. As a result, for a period ending in 1999, Pluto was actually closer to the sun than Neptune.

notes for Pluto

There is some debate among astronomers as to whether Pluto should really be classified as a planet or should instead be considered a large asteroid-like body.
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.