noun the shape of a half-moon; a crescent.
2. half-moon ·noun the moon at the quarters, when half its disk appears illuminated.
3. half-moon ·noun an outwork composed of two faces, forming a salient angle whose gorge resembles a half-moon;
now called a ravelin.
4. half-moon ·noun a marine, sparoid, food fish of california (caesiosoma californiense). the body is ovate, blackish above, blue or gray below. called also medialuna.