Webster's Dictionary 
(1): ( n.) A genus of wading birds comprising the wood ibises.
(2): ( n.) 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.
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
a Greek mythological character, was, according to some, a son of Zeus, or, according to others, of T'molus. All traditions agree in stating that he was a wealthy king, but assign him to different kingdoms, as Lydia, Sipylus, in Plhrygia or Paphlagonia, and Argos or Corinth. Tantalus is peculiarly celebrated in ancient story for the severe punishment inflicted upon him after his death. The following are some of the traditions, of which the most common is that Zeus invited him to his table and communicated his divine counsels to him. Tantalus divulged these secrets, and the gods punished him by placing him in the midst of a lake, of which he could never drink, the water always withdrawing when he stooped. Branches laden with fruit hung temptingly near, but withdrew whenever he reached after them. Over his head there was suspended a huge rock ever threatening to crush him. Another tradition relates that, wishing to try the gods, he cut his son Pelops in pieces, boiled them, and set them before the gods as a repast. A third account states that Tantalus stole nectar and ambrosia from the table of the gods, and gave them to his friends; while a fourth relates the following story. Rhea caused the infant Zeus and his nurse to be guarded by a golden dog, whom subsequently Zeus appointed guardian of his temple in Crete. Pandrerus stole the dog, and carrying him to Mount Sipylus, in Lydia, gave him to Tantalus to take care of. But when Pandaerus demanded the dog back, Tantalus took an oath that he had never received him. The punishment of Tantalus was proverbial in ancient times, and from it the English language has borrowed the verb "to tantalize," that is, to hold out hopes or prospects which can never be realized. (See Ixion).
The Nuttall Encyclopedia 
In the Greek mythology a Lydian king, who, being admitted from blood relationship to the banquets of the gods, incurred their displeasure by betraying their secrets, and was consigned to the nether world and compelled to suffer the constant pangs of hunger and thirst, though he stood up to the chin in water, and had ever before him the offer of the richest fruits, both of which receded from him as he attempted to reach them, while a huge rock hung over him, ever threatening to fall and crush him with its weight.