The Collaborative International Dictionary of English v.0.48:

Cancer \Can"cer\, n. [L. cancer, cancri, crab, ulcer, a sign of
   the zodiac; akin to Gr. karki`nos, Skr. karka[.t]a crab, and
   prob. Skr. karkara hard, the crab being named from its hard
   shell. Cf. Canner, Chancre.]
   1. (Zool.) A genus of decapod Crustacea, including some of
      the most common shore crabs of Europe and North America,
      as the rock crab, Jonah crab, etc. See Crab.
      [1913 Webster]

   2. (Astron.)
      (a) The fourth of the twelve signs of the zodiac. The
          first point is the northern limit of the sun's course
          in summer; hence, the sign of the summer solstice. See
          Tropic.
      (b) A northern constellation between Gemini and Leo.
          [1913 Webster]

   3. (Med.) Formerly, any malignant growth, esp. one attended
      with great pain and ulceration, with cachexia and
      progressive emaciation. It was so called, perhaps, from
      the great veins which surround it, compared by the
      ancients to the claws of a crab. The term is now
      restricted to such a growth made up of aggregations of
      epithelial cells, either without support or embedded in
      the meshes of a trabecular framework.
      [1913 Webster]

   Note: Four kinds of cancers are recognized: (1) Epithelial
         cancer, or Epithelioma, in which there is no
         trabecular framework. See Epithelioma. (2) Scirrhous
         cancer, or Hard cancer, in which the framework
         predominates, and the tumor is of hard consistence and
         slow growth. (3) Encephaloid cancer, Medullary
         cancer, or Soft cancer, in which the cellular
         element predominates, and the tumor is soft, grows
         rapidy, and often ulcerates. (4) Colloid cancer, in
         which the cancerous structure becomes gelatinous. The
         last three varieties are also called carcinoma.
         [1913 Webster]

   Cancer cells, cells once believed to be peculiar to
      cancers, but now know to be epithelial cells differing in
      no respect from those found elsewhere in the body, and
      distinguished only by peculiarity of location and
      grouping.

   Cancer root (Bot.), the name of several low plants, mostly
      parasitic on roots, as the beech drops, the squawroot,
      etc.

   Tropic of Cancer. See Tropic.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

carcinoma \car`ci*no"ma\ (k[aum]r`s[i^]*n[=o]"m[.a]), n. [L.,
   fr. Gr. karki`nwma, fr. karki`nos crab, cancer. See -oma.]
   (Med.)
   A form of malignant cancer arising from epithelial tissue.
   The term was earlier applied to all forms of cancer, or to
   certain non-malignant forms. It is contrasted with sarcoma,
   a malignant form of cancer arising from connective tissue.
   See Cancer. --Dunglison. --Stedman.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

carcinoma
    n 1: any malignant tumor derived from epithelial tissue; one of
         the four major types of cancer

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "carcinoma":
   benign tumor, callosity, callus, cancer, corn, cyst, excrescence,
   fungosity, fungus, growth, intumescence, malignant growth,
   metastatic tumor, mole, morbid growth, neoplasm, nevus,
   nonmalignant tumor, outgrowth, proud flesh, sarcoma, tumor,
   verruca, wart, wen