gargantuan

Merriam-Webster's Word of the Day for November 19, 2011 is:

gargantuan • \gahr-GAN-chuh-wuh\  • adjective
: tremendous in size, volume, or degree : gigantic, colossal

Examples:
The town's wealthiest family lived in a gargantuan mansion at the top of the hill, complete with twelve bedrooms, two swimming pools and a tennis court.

"Contrary to my expectations, I did not have nightmares about gargantuan squid tangling with enormous ichthyosaurs in the shadowy reaches of the sea last night." -- From a blog post by Brian Switek at Wired.com, October 12, 2011

Did you know?
"Gargantua" is the name of a giant king in François Rabelais's 16th-century satiric novel Gargantua. All of the details of Gargantua's life befit a giant. He rides a colossal mare whose tail switches so violently that it fells the entire forest of Orleans. He has an enormous appetite -- in one memorable incident, he inadvertently swallows five pilgrims while eating a salad. The scale of everything connected with Gargantua gave rise to the adjective "gargantuan," which since Shakespeare's time has been used of anything of tremendous size or volume.