Misery
bleak
Stygian.
bleak
An antonym is a word that means the OPPOSITE of another word. The word that means the opposite of light is dark.
Depressing
gloomy, dark
lowering
This rainy weather has made everything so dark, depressing and gloomy.
The chambers of the castle were dark and gloomy. Just because our team lost, there is no need to be gloomy and dejected.
glad
The likely word is "gloomy" (dark, or dismal).
The word is Stygian.