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[ploo-toh] /ˈplu toʊ/
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 2100 miles (3300 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. Until 2006, Pluto was classified as a planet ninth in order from the sun; the International Astronomical Union has reclassified it as a dwarf planet. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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Examples from the Web for Pluto
Contemporary Examples
Historical Examples
  • She begged of him to command his brother Pluto to return her daughter to her.

    Classic Myths Mary Catherine Judd
  • Jupiter, on the other hand, urged Ceres to consent to her remaining as the wife of Pluto.

    Pyrrhus Jacob Abbott
  • Such notes, as, warbled to the string, Drew iron tears down Pluto's cheek.

  • Pluto, suspecting that something had gone wrong, had slipped his halter.

    Nine Little Goslings Susan Coolidge
  • This was the dog Cerberus, who never sleeps, and guards the palace of Pluto night and day.

    Gods and Heroes R. E. Francillon
British Dictionary definitions for Pluto


(classical myth) the god of the underworld; Hades


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
Latin, from Greek Ploutōn, literally: the rich one


the code name of pipelines laid under the English Channel to supply fuel to the Allied forces landing in Normandy in 1944
Word Origin
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
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Word Origin and History for Pluto

Roman god of the underworld, brother of Zeus and Neptune, from Latin Pluto, Pluton, from Greek Plouton "god of wealth," literally "wealth, riches," probably originally "overflowing," from PIE *pleu- "to flow" (see pluvial). 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.

Online Etymology Dictionary, © 2010 Douglas Harper
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Pluto in Science
The ninth and usually farthest planet from the Sun as well as the smallest in size, with a diameter about one-sixth that of Earth. 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 and became, temporarily, the eighth planet in distance from the Sun. Because of its small size (it is smaller than Earth's moon) and the unusual eccentricity and inclination of its orbit, many astronomers have questioned whether it should be regarded as a planet at all, suggesting that Pluto and its moon, Charon, are actually large Kuiper belt objects. See Table at solar system.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Pluto in Culture

Pluto definition

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

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

Pluto definition

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)

Note: 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.
Note: 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.
Note: 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 American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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