Source : Webster's Revised Unabridged Dictionary (1913)

Gargantuan \Gar*gan"tu*an\ (?; 135), a. [From Gargantua, an
   allegorical hero of Rabelais.]
   Characteristic of Gargantua, a gigantic, wonderful personage;
   enormous; prodigious; inordinate.

Source : WordNet®

gargantuan
     adj : of great mass; huge and bulky; "a jumbo jet"; "jumbo shrimp"
           [syn: {elephantine}, {giant}, {jumbo}]