pluto
n. countablen. a small, cold world at the edge of our solar system. It was once called the ninth planet, but scientists now call it a dwarf planet.
n. a dwarf planet in the Kuiper belt, formerly classified as the ninth planet from the Sun. When capitalised, it also refers to the Roman god of the underworld.
Pluto is much smaller than the Earth's moon.
In 2006, astronomers reclassified Pluto as a dwarf planet because it has not cleared its neighboring region of other objects.
The New Horizons mission provided the first high-resolution images of Pluto, revealing a surprisingly complex surface of nitrogen ice mountains and a vast, heart-shaped plain.
From Middle English Pluto, Pluton, from Latin Plūtō, from Ancient Greek Πλούτων (Ploútōn, “god of the underworld”). Doublet of Plouton. Venetia Burney is often credited as having suggested the name for the celestial body.
Always capitalised when referring to the celestial body or the mythological figure.