pluto

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"ol.), 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]

Source: The Collaborative International Dictionary of English