Sentence:  He added not; and Satan bowing low / His gray diſſimulation, diſappear'd / Into thin Air diffuſ'd: for now began / Night with her <WSD>ſullen</WSD> wing to double-ſhade / The Deſert; Fowls in thir clay neſts were couch't; / And now wild Beaſts came forth the woods to roam. 
Meaning of the word marked with <WSD> tags:  Gloomy; dismal; foreboding.