Real Dictionary

black hole
If you say that something, especially money, has gone into a black hole, you mean that it has disappeared and cannot be recovered.
countable noun: Black holes are areas in space where gravity is so strong that nothing, not even light, can escape from them. Black holes are thought to be formed by collapsed stars.

Black Hole in American English
a celestial object or dark region in space, perhaps formed by the collapse of a large star, with such a great mass that its gravitational field will not let even light escape
a small dungeon at Calcutta: it was once believed that over 100 Europeans were confined there one night in 1756 by their Indian captors and died from heat and lack of air
noun: a small prison cell in Fort William, Calcutta (now Kolkata), in which, in 1756, Indian troops are said to have imprisoned 146 Europeans, only 23 of whom were alive the following morning
noun: a theoretical massive object, formed at the beginning of the universe or by the gravitational collapse of a star exploding as a supernova, whose gravitational field is so intense that no electromagnetic radiation can escape

black hole in British English
noun: an object in space so dense that its escape velocity exceeds the speed of light