dark

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Lacking or having very little light.
• adjective Lacking brightness.
• adjective Reflecting only a small fraction of incident light; tending toward black.
• adjective Served without milk or cream.
• adjective Being or having a complexion that is not light in color.
• adjective Sullen or threatening.
• adjective Characterized by gloom or pessimism; dismal or bleak.
• adjective Being or characterized by morbid or grimly satiric humor.
• adjective Unknown or concealed; mysterious.
• adjective Lacking enlightenment, knowledge, or culture.
• adjective Evil in nature or effect; sinister.
• adjective Morally corrupt; vicious.
• adjective Having richness or depth.
• adjective Not giving performances; closed.
• adjective Linguistics Pronounced with the back of the tongue raised toward the velum. Used of the sound (l) in words like full.
• noun Absence of light.
• noun A place having little or no light.
• noun Night; nightfall.
• noun A deep hue or color.
• noun Pieces of laundry having a dark color.
• idiom (in the dark) In secret.
• idiom (in the dark) In a state of ignorance; uninformed.

from The Century Dictionary.

• In the dark; without light.
• To grow or become dark; darken.
• To remain in the dark; lurk; lie hidden or concealed.
• To make dark; darken; obscure.
• Without light; marked by the absence of light; unilluminated; shadowy: as, a dark night; a dark room.
• Not radiating or reflecting light; wholly or partially black or gray in appearance; having the quality opposite to light or white: as, a dark object; a dark color.
• Not fair: applied to the complexion: as, the dark-skinned races.
• Lacking in light or brightness; shaded; obscure: as, a dark day; the dark recesses of a forest.
• Characterized by or producing gloom; dreary; cheerless: as, a dark time in the affairs of the country.
• Threatening; frowning; gloomy; morose: as, a dark scowl.
• Obscure; not easily perceived or understood; difficult to interpret or explain: as, a dark saying; a dark passage in an author.
• Hence Concealed; secret; mysterious; inscrutable as, keep it dark.
• Blind; sightless.
• Unenlightened, either mentally or spiritually; characterized by backwardness in learning, art, science, or religion; destitute of knowledge or culture; ignorant; uninstructed; rude: uncivilized: as, the dark places of the earth; the dark ages.
• Morally black; atrocious; wicked; sinister.
• noun The absence of light; darkness.
• noun A dark place.
• noun A dark hue; a dark spot or part.
• noun A state of concealment; secrecy: as, things done in the dark.
• noun An obscured or unenlightened state or condition; obscurity; a state of ignorance: as, I am still in the dark regarding his intentions.
• noun An obsolete form of darg.

from the GNU version of the Collaborative International Dictionary of English.

• noun Absence of light; darkness; obscurity; a place where there is little or no light.
• noun The condition of ignorance; gloom; secrecy.
• noun (Fine Arts) A dark shade or dark passage in a painting, engraving, or the like.