Brobdingnagian

Brobdingnagian \brob-ding-NAG-ee-uhn\, adjective:
Of extraordinary size; gigantic; enormous.

Brobdingnagian is from Brobdingnag, a country of giants in Swift's Gulliver's Travels.

I can honestly say I've never heard anyone use this word in the course of normal conversation. I am also almost willing to bet I've never read the word in any of the types of books I'm prone to reading. And, no, I've never read Gulliver's Travels. It just never appealed to me much. I can't tell you why. It's just a reaction I have to some books or some authors.