The Collaborative International Dictionary of English v.0.48:

Caul \Caul\ (k[add]l), n. [OE. calle, kelle, prob. fr. F. cale;
   cf. Ir. calla a veil.]
   1. A covering of network for the head, worn by women; also, a
      net. --Spenser.
      [1913 Webster]

   2. (Anat.) The fold of membrane loaded with fat, which covers
      more or less of the intestines in mammals; the great
      omentum. See Omentum.
      [1913 Webster]

            The caul serves for the warming of the lower belly.
                                                  --Ray.
      [1913 Webster]

   3. A part of the amnion, one of the membranes enveloping the
      fetus, which sometimes is round the head of a child at its
      birth; -- called also a veil.
      [1913 Webster +PJC]

            It is deemed lucky to be with a caul or membrane
            over the face. This caul is esteemed an infallible
            preservative against drowning . . . According to
            Chrysostom, the midwives frequently sold it for
            magic uses.                           --Grose.
      [1913 Webster]

            I was born with a caul, which was advertised for
            sale, in the newspapers, at the low price of fifteen
            guineas.                              --Dickens.
      [1913 Webster]

WordNet (r) 3.0 (2006):

caul
    n 1: part of the peritoneum attached to the stomach and to the
         colon and covering the intestines [syn: greater omentum,
         gastrocolic omentum, caul]
    2: the inner membrane of embryos in higher vertebrates
       (especially when covering the head at birth) [syn: caul,
       veil, embryonic membrane]

Easton's 1897 Bible Dictionary:

Caul
   (Heb. yothe'reth; i.e., "something redundant"), the membrane
   which covers the upper part of the liver (Ex. 29:13, 22; Lev.
   3:4, 10, 15; 4:9; 7:4; marg., "midriff"). In Hos. 13:8 (Heb.
   seghor; i.e., "an enclosure") the pericardium, or parts about
   the heart, is meant.