The Collaborative International Dictionary of English v.0.48:

Krishna \Krish"na\ (kr[i^]sh"n[.a]), n. [Skr. k[.r]sh[.n]a ' The
   black.'.] (Hindu Myth.)
   The most popular of the Hindu divinities, usually held to be
   the eighth incarnation of the god Vishnu.
   [1913 Webster]

   Note: Krishna is a well-known Hindu deity. Originally the
         ethnic god of some powerful confederation of Rajput
         clans, by fusion with the Vishnu of the older theology
         Krishna becomes one of the chief divinities of
         Hinduism. He is indeed an avatar of Vishnu, or Vishnu
         himself. In his physical character mingle myths of
         fire, lightning, and storm, of heaven and the sun. In
         the epic he is a hero invincible in war and love,
         brave, but above all crafty. He was the son of Vasudeva
         and Devaki, and born at Mathura, on the Yamuna, between
         Delhi and Agra, among the Yadavas. Like that of many
         solar heroes, his birth was beset with peril. On the
         night when it took place, his parents had to remove him
         from the reach of his uncle, King Kansa, who sought his
         life because he had been warned by a voice from heaven
         that the eighth son of Devaki would kill him, and who
         had regularly made away with his nephews at their
         birth. Conveyed across the Yamuna, Krishna was brought
         up as their son by the shepherd Nanda and his wife
         Yashoda, together with his brother Balarama, 'Rama the
         strong,' who had been likewise saved from massacre. The
         two brothers grew up among the shepherds, slaying
         monsters and demons and sporting with the Gopis, the
         female cowherds of Vrindavana. Their birth and infancy,
         their juvenile exploits, and their erotic gambols with
         the Gopis became in time the essential portion of the
         legend of Krishna, and their scenes are today the most
         celebrated centers of his worship. When grown, the
         brothers put their uncle Kansa to death, and Krishna
         became king of the Yadavas. He cleared the land of
         monsters, warred against impious kings, and took part
         in the war of the sons of Pandu against those of
         Dhritarashtra, as described in the Mahabharata. He
         transferred his capital to Dvaraka ('the city of
         gates'), the gates of the West, since localized in
         Gujarat. There he and his race were overtaken by the
         final catastrophe. After seeing his brother slain, and
         the Yadavas kill each other to the last man, he himself
         perished, wounded in the heel, like Achilles, by the
         arrow of a hunter. The bible of the worshipers of
         Vishnu in his most popular manifestation, that of
         Krishna, consists of the Bhagavatapurana and the
         Bhagavadgita. See these words.
         [Century Dict. 1906]

   Hare Krishnas A popular name for the group International
      Society for Krishna Consciousness (abbreviated ISKCON),
      devotees of Krishna, founded in 1966 by A. C.
      Bhaktivedanta Swami Prabhupada (born 1896, died 1977).
      They are called thus because of their frequent public
      chanting of the words "Hare Krishna".
      [PJC]

WordNet (r) 3.0 (2006):

International Society for Krishna Consciousness
    n 1: a religious sect founded in the United States in 1966;
         based on Vedic scriptures; groups engage in joyful chanting
         of `Hare Krishna' and other mantras based on the name of
         the Hindu god Krishna; devotees usually wear saffron robes
         and practice vegetarianism and celibacy [syn: Hare
         Krishna, International Society for Krishna
         Consciousness, ISKCON]