Source : Webster's Revised Unabridged Dictionary (1913)

Jehovah \Je*ho"vah\, n. [Heb. usually y[e^]h[=o]v[=a]h (with the
   vowel points of [a^]d[=o]n[=a]i Lord), sometimes (to avoid
   repetition) y[e^]h[=o]vih (with the vowel points of
   [e^]l[=o]h[=i]m God); but only the four Heb, consonants yhvh
   are conceded to be certainly known.]
   A Scripture name of the Supreme Being, by which he was
   revealed to the Jews as their covenant God or Sovereign of
   the theocracy; the ``ineffable name'' of the Supreme Being,
   which was not pronounced by the Jews.

Yahweh \Yah"weh\, Yahwe \Yah"we\, n. Also Jahveh \Jah"veh\,
Jahve \Jah"ve\, etc.
   A modern transliteration of the Hebrew word translated
   {Jehovah} in the Bible; -- used by some critics to
   discriminate the tribal god of the ancient Hebrews from the
   Christian Jehovah. Yahweh or {Yahwe} is the spelling now
   generally adopted by scholars.

Source : WordNet®

Jehovah
     n 1: a name for the God of the Old Testament as transliterated
          from the Hebrew consonants YHVH [syn: {Yahweh}, {YHWH},
          {Yahwe}, {Yahveh}, {YHVH}, {Yahve}, {Wahvey}, {Jahvey},
          {Jahweh}, {JHVH}]
     2: terms referring to the Judeo-Christian God [syn: {Godhead},
        {Lord}, {Creator}, {Maker}, {Divine}, {God Almighty}, {Almighty}]