Main Entry: Plu·to

Pronunciation: \ˈplü-(ˌ)tō\

Function: noun

Etymology: Latin Pluton-, Pluto, from Greek Ploutōn

Date: 14th century

1 : the Greek god of the underworld — compare dis
2 [New Latin] : a dwarf planet occupying an orbit that crosses the orbit of Neptune

usage In 2006 the International Astronomical Union defined planet in such a way as to exclude Pluto, reclassifying it instead as a dwarf planet. Although discussion of the matter continues, the change has been widely accepted.