Source : Webster's Revised Unabridged Dictionary (1913)

Tropic \Trop"ic\, n. [F. tropique, L. tropicus of or belonging
   to a turn, i. e., of the sun, Gr. ? of the solstice, ? (sc.
   ?) the tropic or solstice, fr. ? to turn. See {Trope}.]
   1. (Astron.) One of the two small circles of the celestial
      sphere, situated on each side of the equator, at a
      distance of 23[deg] 28[min], and parallel to it, which the
      sun just reaches at its greatest declination north or
      south, and from which it turns again toward the equator,
      the northern circle being called the {Tropic of Cancer},
      and the southern the {Tropic of Capricorn}, from the names
      of the two signs at which they touch the ecliptic.

   2. (Geog.)
      (a) One of the two parallels of terrestrial latitude
          corresponding to the celestial tropics, and called by
          the same names.
      (b) pl. The region lying between these parallels of
          latitude, or near them on either side.

                The brilliant flowers of the tropics bloom from
                the windows of the greenhouse and the saloon.
                                                  --Bancroft.

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. (Zo["o]l.) 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}.

   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.

   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.

   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, Medullary, 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}.

   {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}.

Source : WordNet®

Tropic of Cancer
     n : a line of latitude about 23 degrees North of the equator