a small planet and the farthest known planet from the sun; has the most elliptical orbit of all the planets; "Pluto was discovered by Clyde Tombaugh in 1930"
(Greek mythology) the god of the underworld in ancient mythology; brother of Zeus and husband of Persephone
having substance or capable of being treated as fact; not imaginary; "the substantial world"; "a mere dream, neither substantial nor practical"; "most ponderous and substantial things"- Shakespeare
having a firm basis in reality and being therefore important, meaningful, or considerable; "substantial equivalents"