BLACK HOLE, noun. A gravitationally domineering celestial body with an event horizon from which even light cannot escape; the most dense material in the universe, condensed into a singularity, usually formed by a collapsing massive star.

BLACK HOLE, noun. (figuratively) A void into which things disappear and/or from which nothing emerges.

BLACK HOLE, noun. A sphere of influence into which or from which communication or similar activity is precluded.

BLACK HOLE, noun. An entity which consumes time or resources without demonstrable utility.

BLACK HOLE, noun. A dungeon or dark cell in a prison; a military lock-up or guardroom.