The Collaborative International Dictionary of English v.0.48:
Tantalus \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. (Zool.) A genus of wading birds comprising the wood
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.