A postage stamp illustration of a cachalot or sperm whale.
sperm whale definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
any of a family (Physeteridae) of toothed whales; esp., a large species (Physeter catodon) inhabiting warm seas: a closed cavity in its roughly square head contains sperm oil
sperm whale definition by American Heritage Dictionary
Any of several large, toothed whales of the family Physeteridae, especially Physeter catodon or P. macrocephalus, of tropical and temperate oceans, whose massive head has a cavity containing sperm oil and spermaceti and whose long intestines often contain ambergris. Also called cachalot.