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Pluto Plu"to, [Also spelled {rop. .]n. [L., fr. Gr. ?.] 1. (Class. Myth.) The son of Saturn and Rhea, brother of Jupiter and Neptune; the dark and gloomy god of the Lower World. [1913 Webster]

2. The ninth planet of the Solar System, the smallest (5700 km radius) and most distant from the sun. The suggestion has been made that it more closely resembles a large close comet than a planet. Its orbit has an eccentricity of 0.248, larger than that of any other planet; it varies from 4.44 to 7.37 billion km distance from the sun. [PJC]

Pluto is an oddball among its eight sister planets. It's the smallest in both size and mass, and has the most elliptical orbit. It moves in a plane tilted markedly away from the other planets' orbits. Moreover, Pluto is the only planet made almost entirely of ice. --Ron Cohen (Science News, Feb. 27, 1999, p. 139)

{Pluto monkey} (Zo["o]l.), a long-tailed African monkey ({Cercopithecus pluto}), having side whiskers. The general color is black, more or less grizzled; the frontal band is white. [1913 Webster]