Definition of "stygian"

stygian

/ˈstɪd͡ʒ.i.ən/

adjective
comparative more stygian, superlative most stygian
1. Alternative form of Stygian (“of or relating to the river Styx”)
2. (literary) Dark and gloomy.
  Quotations
  The things which the Stygian darkness hid from my objective eye […]
  1913 January–May, Edgar Rice Burroughs, “The Gods of Mars”, in The All-Story, New York, N.Y.: Frank A. Munsey Co.; republished as The Gods of Mars, Chicago, Ill.: A[lexander] C[aldwell] McClurg & Co., 1918 September, page 184
3. (literary) Infernal or hellish.
4. (vision, of a perceived color) Having a luminosity below 0%.