\Lu"nule\, n. [F., fr. L. lunula, dim. of luna moon.]
1. (Anat.) Anything crescent-shaped; a crescent-shaped part
   or mark; a lunula, a lune.
2. (Chem.) A lune. See {Lune}.
3. (Zo["o]l.)
   (a) A small or narrow crescent.
   (b) 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}.