adj

• Having an absolute or (more often) relative lack of light.
  "Dark signals should be treated as all-way stop signs."
• (of colour) Dull or deeper in hue; not bright or light.
  "My sister’s hair is darker than mine."
• Marked by or conducted with secrecy.
  "The first favourite was never heard of, the second favourite was never seen after the distance post, all the ten-to-oners were in the rear, and a dark horse which had never been thought of, and which the careless St. James had never even observed in the list, rushed past the grand stand in sweeping triumph."
• (of a time period) Lacking progress in science or the arts.
  "The dark ages began after the collapse of the Roman Empire."

noun

• (uncountable) Ignorance.
  "We kept him in the dark."
• (uncountable) Nightfall.
  "It was after dark before we got to playing baseball."

verb

• (intransitive) To grow or become dark, darken.
• (intransitive) To remain in the dark, lurk, lie hidden or concealed.
  "To dark is still used in Swaledale (Yorkshire) in the sense of to lie hid, as, 'Te rattens [rats] mun ha bin darkin whel nu [till now]; we hannot heerd tem tis last fortnith'."
• (transitive) To make dark, darken; to obscure.