The Collaborative International Dictionary of English v.0.48:

Sperm \Sperm\, n.[Contr. fr. spermaceti.]
   Spermaceti.
   [1913 Webster]

   Sperm oil, a fatty oil found as a liquid, with spermaceti,
      in the head cavities of the sperm whale.

   Sperm whale. (Zool.) See in the Vocabulary.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sperm whale \Sperm" whale`\ (Zool.)
   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.
   [1913 Webster]

   Pygmy sperm whale (Zool.), 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.

   Sperm-whale porpoise (Zool.), a toothed cetacean
      (Hyperoodon 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.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sperm whale
    n 1: large whale with a large cavity in the head containing
         spermaceti and oil; also a source of ambergris [syn: sperm
         whale, cachalot, black whale, Physeter catodon]