noun

• (medicine, oncology, pathology) A disease in which the cells of a tissue undergo uncontrolled (and often rapid) proliferation.
  "If successful, Edison and Ford—in 1914—would move society away from the[…]hazards of gasoline cars: air and water pollution, noise and noxiousness, constant coughing and the undeniable rise in cancers caused by smoke exhaust particulates."
• (figuratively) Something damaging that spreads throughout something else.
  "The disease of the self runs through my blood; It's a cancer fatal to my soul."

adj

• (slang) Extremely unpleasant and annoying.
  "I used to love this game, but the new meta is straight up cancer."

name

• (astronomy) A constellation of the zodiac supposedly shaped like a crab.
  "And add more coals to Cancer when he burns / With entertaining great Hyperion."
• (astrology) The zodiac sign for the crab, ruled by the Moon and covering June 22–July 22 (tropical astrology) or July 16–August 15 (sidereal astrology).