A caul is a membrane or thin piece of skin that sometimes covers a newborn baby's head. The caul is part of the anmniotic sac that protects a fetus before birth.

Most mammals are enclosed within a protective membrane before they're born, and when part of this membrane is attached to a newborn, it's called a caul. Possibly because it's so rare for a baby to be born with this caul covering his or her head, it's been considered good luck since medieval times. The word once referred to a woman's close-fitting hat, from the French word cale, "cap," with a Latin root, calautica, "type of women's headdress."

Definitions of caul
  1. noun
    the inner membrane of embryos in higher vertebrates (especially when covering the head at birth)
    synonyms: embryonic membrane, veil
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    type of:
    fetal membrane
    any membrane that functions for the protection or nourishment or respiration or excretion of a developing fetus
  2. noun
    part of the peritoneum attached to the stomach and to the colon and covering the intestines
    synonyms: gastrocolic omentum, greater omentum
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    type of:
    a fold of peritoneum supporting the viscera
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