adjective.
So great in scope, degree, or importance as to amaze.
adjective.
Extremely large in amount, extent, or size; enormous.
adjective.
Remarkable; outstanding.
The Century Dictionary and Cyclopedia
Causing stupor or astonishment; astounding; amazing; specifically, astonishing from greatness in extent or degree; of wonderful magnitude; immense; prodigious: as, a stupendous work of nature or art; a stupendous blunder.
the GNU version of the Collaborative International Dictionary of English
adjective.
Astonishing; wonderful; amazing; especially, astonishing in magnitude or elevation.