mammoth

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various extinct elephants of the genus Mammuthus of the Pliocene, Pleistocene, and Holocene Epochs, having ridged molars and often, as in the woolly mammoth, long tusks and hair.
• noun Something that is of great size.
• adjective Of enormous size, extent, or amount; huge. synonym: enormous.
• adjective Of great scope or importance.

from The Century Dictionary.

• noun An extinct species of elephant, Elephas primigenius.
• Of great comparative size, like a mammoth; gigantic; colossal; immense: as, a mammoth ox; the mammoth tree of California (Sequoia gigantea).

from the GNU version of the Collaborative International Dictionary of English.

• adjective Resembling the mammoth in size; very large; gigantic.
• noun (Zoöl.) An extinct, hairy, maned elephant (Mammuthus primigenius formerly Elephas primigenius), of enormous size, remains of which are found in the northern parts of both continents. The last of the race, in Europe, were coeval with prehistoric man.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A large, hairy, extinct elephant-like mammal of the taxonomic genus Mammuthus.
• noun figuratively Something very large of its kind.
• adjective Very large.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective so exceedingly large or extensive as to suggest a giant or mammoth
• noun any of numerous extinct elephants widely distributed in the Pleistocene; extremely large with hairy coats and long upcurved tusks