WordNet sense 1 (the time after sunset and before sunrise while it is dark outside):

night, nighttime

WordNet sense 2 (absence of moral or spiritual values):

darkness, iniquity, wickedness

WordNet sense 3 (an unilluminated area):

shadow

WordNet sense 4 (hidden on any grounds for any motive):

concealed

WordNet sense 5 (showing a brooding ill humor):

dour, glowering, glum, moody, morose, saturnine, sour, sullen

WordNet sense 6 (having an irritable and unpleasant disposition):

ill-natured

WordNet sense 7 (stemming from evil characteristics or forces; wicked or dishonorable):

sinister

WordNet sense 8 (morally bad or wrong):

evil

WordNet sense 9 (lacking enlightenment or knowledge or culture):

benighted

WordNet sense 10 (not enlightened; ignorant):

unenlightened

WordNet sense 11 (marked by difficulty of style or expression):

obscure

WordNet sense 12 (difficult to understand):

incomprehensible, uncomprehensible

WordNet sense 13 (causing dejection):

blue, depressing, dingy, disconsolate, dismal, drab, drear, dreary, grim, sorry, dispiriting, dingy

WordNet sense 14 (lacking cheer; depressing):

uncheerful

WordNet sense 15 (slightly dark):

darkish

WordNet sense 16 (dark and gloomy):

tenebrous

WordNet sense 17 (without illumination):

lightless

WordNet sense 18 (depressingly dark):

gloomy, sulky, gloomful, glooming

WordNet sense 19 (lighted by or as if by twilight):

dusky, twilight

WordNet sense 20 (lacking in light; not bright or harsh):

dim

WordNet sense 21 (like twilight; dim):

crepuscular

WordNet sense 22 (intensely dark and gloomy as with perpetual darkness):

Cimmerian

WordNet sense 23 (dark and misty and gloomy):

caliginous

WordNet sense 24 (extremely dark):

black, pitch-black, pitch-dark

WordNet sense 25 (marked by dark or relatively dark pigmentation of hair or skin or eyes):

brunette

WordNet sense 26 (having skin rich in melanin pigments):

colored, coloured, dark-skinned, non-white

WordNet sense 27 (lacking activity; lying idle or unused):

inactive