The Collaborative International Dictionary of English v.0.48:

Ambergris \Am"ber*gris\ ([a^]m"b[~e]r*gr[=e]s), n. [F. ambre
   gris, i. e., gray amber; F. gris gray, which is of German
   origin: cf. OS. gr[^i]s, G. greis, gray-haired. See Amber.]
   A substance of the consistence of wax, found floating in the
   Indian Ocean and other parts of the tropics, and also as a
   morbid secretion in the intestines of the sperm whale
   (Physeter macrocephalus), which is believed to be in all
   cases its true origin. In color it is white, ash-gray,
   yellow, or black, and often variegated like marble. The
   floating masses are sometimes from sixty to two hundred and
   twenty-five pounds in weight. It is wholly volatilized as a
   white vapor at 212[deg] Fahrenheit, and is highly valued in
   perfumery. --Dana.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ambergris
    n 1: waxy substance secreted by the sperm whale and found
         floating at sea or washed ashore; used in perfume

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "ambergris":
   ambrosia, aromatic, aromatic gum, aromatic water, attar,
   attar of roses, balm, balm of Gilead, balsam, bay oil,
   bergamot oil, champaca oil, civet, essence, essential oil, extract,
   fixative, heliotrope, jasmine oil, lavender oil, musk, myrcia oil,
   myrrh, parfum, perfume, perfumery, rose oil, scent, volatile oil