Definition of "dark" []

• Lacking or having very little light: a dark corner. (adjective)
• Lacking brightness: a dark day. (adjective)
• Reflecting only a small fraction of incident light. (adjective)
• Of a shade tending toward black in comparison with other shades. Used of a color. (adjective)
• Having a complexion that is not fair; swarthy. (adjective)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "~ Measuring the unseeable: Researchers probe proteins' 'dark energy' -- Researchers at the University of Pennsylvania School of Medicine are the first to observe and measure the internal motion inside proteins, or its “dark energy."
• "He would feel and cry out to her, 'Let me tell you alone, if I must tell it, and _in the dark, in the dark_!' when he could not see the heart-breaking shame grow upon her face, nor see his own guilty face reflected in her eyes."
• "Or when the substances are consumed _as solids_, then the spectral effects are reversed, and the lines that would be dark lines in the luminous colored spectrum become themselves luminous lines on the screen; but these lines hold the same relation in mathematical measurement, etc., as do the _dark_ lines in the colored spectrum."