Tantalus's cup

Related to Tantalus's cup: Torment of Tantalus
(Physics) a philosophical toy, consisting of a cup, within which is the figure of a man, and within the figure a siphon, the longer arm of which passes down through the bottom of the cup, and allows the escape of any liquid that may be poured in, when it reaches as high as the bend of the siphon, which is just below the level of the mouth of the figure in the cup.

See also: Tantalus

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.