Definition of lunule

• n. - Anything crescent-shaped; a crescent-shaped part or mark; a lunula, a lune.
• n. - A lune. See Lune.
• n. - A small or narrow crescent.
• n. - 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.