n. Something which is shaped like a little moon or narrow crescent; a lunule or lunulet.n. Specifically— The free crescentic edge and adjoining thin part of a semilunar valve of the heart.n. The small white semilunar mark at the base of the human fingernails.n. A crescentic impression on some bivalve shells; a lunule.n. A small semicircular or crescentic spot of color; a lunulet.n. [capitalized] A generic name given by Hitchcock to ichnolites of uncertain character.n. In mathematics, a lune.n. In entomology, a small depression on the frons of a dipterous insect.