1.NounAnything crescent-shaped; a crescent-shaped part or mark; a lunula or lune.
"A healthy lunule is usually most prominent on the thumb and may be invisible on the pinky finger.; The architect incorporated a lunule design into the arched windows of the cathedral."
2.NounAn area in front of the beak of many bivalve shells, sometimes shaped like a double crescent, but more often heart-shaped.