Synonyms for Darkening (same or very similar meaning)
WordNet sense 1 (characterized by hopelessness; filled with gloom):
gloomy, grimWordNet sense 2 (without hope because there seems to be no possibility of comfort or success):
hopelessWordNet sense 3 (devoid of or deficient in light or brightness; shadowed or black):
darkWordNet sense 4 (changing to a darker color):
blackeningFrom the ODE community, based on WordNetadd/edit