- Proper noun. (zodiac constellations) A constellation of the zodiac supposedly shaped like a crab.
- Proper noun. (astrology) The Zodiac sign for the crab, ruled by the Moon and covering June 23 - July 23.
- Noun. Someone with a Cancer star sign.
- Noun. (medicine, oncology) A disease in which the cells of a tissue undergo uncontrolled (and often rapid) proliferation.