Source : Webster's Revised Unabridged Dictionary (1913)

Behemoth \Be"he*moth\, n. [Heb. behem[=o]th, fr. Egyptian
   P-ehe-maut hippopotamus.]
   An animal, probably the hippopotamus, described in --Job xl.
   15-24.

Source : WordNet®

behemoth
     n 1: someone or something that is abnormally large and powerful
          [syn: {giant}, {goliath}, {monster}, {colossus}]
     2: a person of exceptional importance and reputation [syn: {colossus},
         {giant}, {heavyweight}, {titan}]