The Collaborative International Dictionary of English v.0.48:

Brobdingnagian \Brob`ding*nag"i*an\, a. [From Brobdingnag, a
   country of giants in "Gulliver's Travels."]
   Colossal; of extraordinary height; gigantic. -- n. A giant.
   [Spelt often Brobdignagian.]
   [1913 Webster]