Source : Webster's Revised Unabridged Dictionary (1913)

Half-moon \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}.

Source : WordNet®

half-moon
     n 1: the crescent-shaped area at the base of the human fingernail
          [syn: {lunula}, {lunule}]
     2: the time at which the moon is at first or last quarter when
        half its face is illuminated