sperm whale

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

• noun A very large toothed whale (Physeter macrocephalus syn. P. catodon) formerly hunted for the spermaceti in its massive head and the ambergris in its intestines.
• noun Either of two small toothed whales (Kogia breviceps or K. sima) also containing spermaceti in the head.

from The Century Dictionary.

• noun The spermaceti-whale or cachalot, Physeter (or Catodon) macrocephalus, belonging to the family Physeteridæ (which see for technical characters; see also cut of skull under Physeter).

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

• (Zoöl.) A very large toothed whale (Physeter macrocephalus), having a head of enormous size. The upper jaw is destitute of teeth. In the upper part of the head, above the skull, there is a large cavity, or case, filled with oil and spermaceti. This whale sometimes grows to the length of more than eighty feet. It is found in the warmer parts of all the oceans. Called also cachalot, and spermaceti whale.
• (Zoöl.) a small whale (Kogia breviceps), seldom twenty feet long, native of tropical seas, but occasionally found on the American coast. Called also snub-nosed cachalot.
• (Zoöl.) a toothed cetacean (Hyperoödon bidens), found on both sides of the Atlantic and valued for its oil. The adult becomes about twenty-five feet long, and its head is very large and thick. Called also bottle-nosed whale.

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

• noun A whale (Physeter macrocephalus), the largest of the toothed whales.

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

• noun large whale with a large cavity in the head containing spermaceti and oil; also a source of ambergris