\Half"-moon`\, n.
1. The moon at the quarters, when half its disk appears
   illuminated.
2. The shape of a half-moon; a crescent.
         See how in warlike muster they appear, In rhombs,
         and wedges, and half-moons, and wings. --Milton.
3. (Fort.) An outwork composed of two faces, forming a
   salient angle whose gorge resembles a half-moon; -- now
   called a {ravelin}.
4. (Zo["o]l.) A marine, sparoid, food fish of California
   ({C[ae]siosoma Californiense}). The body is ovate,
   blackish above, blue or gray below. Called also
   {medialuna}.