The Collaborative International Dictionary of English v.0.48:

Half-moon \Half"-moon`\ (-m[=oo]n`), n.
   1. The moon at the quarters, when half its disk appears
      illuminated.
      [1913 Webster]

   2. The shape of a half-moon; a crescent.
      [1913 Webster]

            See how in warlike muster they appear,
            In rhombs, and wedges, and half-moons, and wings.
                                                  --Milton.
      [1913 Webster]

   3. (Fort.) An outwork composed of two faces, forming a
      salient angle whose gorge resembles a half-moon; -- now
      called a ravelin.
      [1913 Webster]

   4. (Zool.) A marine, sparoid, food fish of California
      (C[ae]siosoma Californiense). The body is ovate,
      blackish above, blue or gray below. Called also
      medialuna.
      [1913 Webster]