Lunule

n.
  1. (Anat.) Anything crescent-shaped; a crescent-shaped part or mark; a lunula; a lune.
  2. (Chem.) A lune. See Lune.
    1. A small or narrow crescent.
    2. A special area in front of the beak of many bivalve shells. It sometimes has the shape of a double crescent, but is oftener heart-shaped. See Illust. of Bivalve.