Pronunciation: (plOO'tō),[key] —n. 1. Class. Myth.a name given to Hades, under which he is identified by the Romans with Orcus.
2. Astron.the planet ninth in order from the sun, 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. See table under planet.