Can·cer n.
 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.
 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  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.
 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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