'Demogorgon' definitions:

Definition of 'Demogorgon'

noun

(Greek mythology) a mysterious and terrifying deity of the underworld

From: GCIDE

Demogorgon \De`mo*gor"gon\ (d[=e]"m[-o]*g[^o]r*g[o^]n or d[e^]m"[-o]*g[^o]r*g[o^]n), n. [First mentioned by Lutatius, or Lactantius Placidus, the scholiast on Statius, perh. fr. Gr. dai`mwn god, deity + gorgo`s fierce, terrible] A mysterious, terrible, and evil divinity, regarded by some as the author of creation, by others as a great magician who was supposed to command the spirits of the lower world. See Gorgon. [1913 Webster]
Orcus and Ades, and the dreaded name Of Demogorgon. --Milton. [1913 Webster]