\Tan"ta*lus\, n. [L., from Gr. Ta`ntalos.] (Gr. Myth.)
1. A Phrygian king who was punished in the lower world by
   being placed in the midst of a lake whose waters reached
   to his chin but receded whenever he attempted to allay his
   thirst, while over his head hung branches laden with
   choice fruit which likewise receded whenever he stretched
   out his hand to grasp them.
2. (Zo["o]l.) A genus of wading birds comprising the wood
   ibises.
{Tantalus's cup} (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.