The Collaborative International Dictionary of English v.0.48:

Sign \Sign\, n. [F. signe, L. signum; cf. AS. segen, segn, a
   sign, standard, banner, also fr. L. signum. Cf. Ensign,
   Resign, Seal a stamp, Signal, Signet.]
   That by which anything is made known or represented; that
   which furnishes evidence; a mark; a token; an indication; a
   proof. Specifically:
   (a) A remarkable event, considered by the ancients as
       indicating the will of some deity; a prodigy; an omen.
   (b) An event considered by the Jews as indicating the divine
       will, or as manifesting an interposition of the divine
       power for some special end; a miracle; a wonder.
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             Through mighty signs and wonders, by the power of
             the Spirit of God.                   --Rom. xv. 19.
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             It shall come to pass, if they will not believe
             thee, neither hearken to the voice of the first
             sign, that they will believe the voice of the
             latter sign.                         --Ex. iv. 8.
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   (c) Something serving to indicate the existence, or preserve
       the memory, of a thing; a token; a memorial; a monument.
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             What time the fire devoured two hundred and fifty
             men, and they became a sign.         --Num. xxvi.
                                                  10.
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   (d) Any symbol or emblem which prefigures, typifles, or
       represents, an idea; a type; hence, sometimes, a picture.
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             The holy symbols, or signs, are not barely
             significative; but what they represent is as
             certainly delivered to us as the symbols
             themselves.                          --Brerewood.
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             Saint George of Merry England, the sign of victory.
                                                  --Spenser.
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   (e) A word or a character regarded as the outward
       manifestation of thought; as, words are the sign of
       ideas.
   (f) A motion, an action, or a gesture by which a thought is
       expressed, or a command or a wish made known.
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             They made signs to his father, how he would have
             him called.                          --Luke i. 62.
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   (g) Hence, one of the gestures of pantomime, or of a language
       of a signs such as those used by the North American
       Indians, or those used by the deaf and dumb.
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   Note: Educaters of the deaf distinguish between natural
         signs, which serve for communicating ideas, and
         methodical, or systematic, signs, adapted for the
         dictation, or the rendering, of written language, word
         by word; and thus the signs are to be distinguished
         from the manual alphabet, by which words are spelled on
         the fingers.
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   (h) A military emblem carried on a banner or a standard.
       --Milton.
   (i) A lettered board, or other conspicuous notice, placed
       upon or before a building, room, shop, or office to
       advertise the business there transacted, or the name of
       the person or firm carrying it on; a publicly displayed
       token or notice.
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             The shops were, therefore, distinguished by painted
             signs, which gave a gay and grotesque aspect to the
             streets.                             --Macaulay.
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   (j) (Astron.) The twelfth part of the ecliptic or zodiac.
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   Note: The signs are reckoned from the point of intersection
         of the ecliptic and equator at the vernal equinox, and
         are named, respectively, Aries ([Aries]), Taurus
         ([Taurus]), Gemini (II), Cancer ([Cancer]), Leo
         ([Leo]), Virgo ([Virgo]), Libra ([Libra]),
         Scorpio ([Scorpio]), Sagittarius ([Sagittarius]),
         Capricornus  ([Capricorn]), {Aquarius ([Aquarius]),
         Pisces ([Pisces]). These names were originally the
         names of the constellations occupying severally the
         divisions of the zodiac, by which they are still
         retained; but, in consequence of the procession of the
         equinoxes, the signs have, in process of time, become
         separated about 30 degrees from these constellations,
         and each of the latter now lies in the sign next in
         advance, or to the east of the one which bears its
         name, as the constellation Aries in the sign Taurus,
         etc.
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   (k) (Alg.) A character indicating the relation of quantities,
       or an operation performed upon them; as, the sign +
       (plus); the sign -- (minus); the sign of division /, and
       the like.
   (l) (Med.) An objective evidence of disease; that is, one
       appreciable by some one other than the patient.
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   Note: The terms symptom and and sign are often used
         synonymously; but they may be discriminated. A sign
         differs from a symptom in that the latter is perceived
         only by the patient himself. The term sign is often
         further restricted to the purely local evidences of
         disease afforded by direct examination of the organs
         involved, as distinguished from those evidence of
         general disturbance afforded by observation of the
         temperature, pulse, etc. In this sense it is often
         called physical sign.
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   (m) (Mus.) Any character, as a flat, sharp, dot, etc.
   (n) (Theol.) That which, being external, stands for, or
       signifies, something internal or spiritual; -- a term
       used in the Church of England in speaking of an ordinance
       considered with reference to that which it represents.
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             An outward and visible sign of an inward and
             spiritual grace.                     --Bk. of
                                                  Common Prayer.
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   Note: See the Table of Arbitrary Signs, p. 1924.
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   Sign manual.
   (a) (Eng. Law) The royal signature superscribed at the top of
       bills of grants and letter patent, which are then sealed
       with the privy signet or great seal, as the case may be,
       to complete their validity.
   (b) The signature of one's name in one's own handwriting.
       --Craig. Tomlins. Wharton.
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   Syn: Token; mark; note; symptom; indication; signal; symbol;
        type; omen; prognostic; presage; manifestation. See
        Emblem.
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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.
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   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.
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   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.
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   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.
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   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.
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WordNet (r) 3.0 (2006):

cancer
    n 1: any malignant growth or tumor caused by abnormal and
         uncontrolled cell division; it may spread to other parts of
         the body through the lymphatic system or the blood stream
         [syn: cancer, malignant neoplastic disease]
    2: (astrology) a person who is born while the sun is in Cancer
       [syn: Cancer, Crab]
    3: a small zodiacal constellation in the northern hemisphere;
       between Leo and Gemini
    4: the fourth sign of the zodiac; the sun is in this sign from
       about June 21 to July 22 [syn: Cancer, Cancer the Crab,
       Crab]
    5: type genus of the family Cancridae [syn: Cancer, genus
       Cancer]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "cancer":
   benign tumor, blast, blight, callosity, callus, canker, carcinoma,
   corn, cyst, dry rot, excrescence, fungosity, fungus, growth,
   intumescence, malignant growth, metastatic tumor, mildew, mold,
   mole, morbid growth, moth, moth and rust, must, neoplasm, nevus,
   nonmalignant tumor, outgrowth, pest, proud flesh, rot, rust,
   sarcoma, smut, tumor, verruca, wart, wen, worm