Roman god of the underworld, brother of Zeus and Neptune, from Latin Pluto, Pluton, from Greek Plouton "god of wealth," literally "wealth, riches," probably originally "overflowing," from PIE *pleu- "to flow" (see pluvial). The planet (since downgraded) was discovered 1930 by C.W. Tombaugh; Minerva also was suggested as a name for it. The cartoon dog first appeared in Walt Disney's "Moose Hunt," released April 1931.