Half-moon \Half"-moon`\ (-m[=oo]n`), n.
   1. The moon at the quarters, when half its disk appears
      illuminated.
      
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   2. The shape of a half-moon; a crescent.
      
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            See how in warlike muster they appear,
            In rhombs, and wedges, and half-moons, and wings.
                                                  --Milton.
      
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   3. (Fort.) An outwork composed of two faces, forming a
      salient angle whose gorge resembles a half-moon; -- now
      called a {ravelin}.
      
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   4. (Zool.) A marine, sparoid, food fish of California
      ({Caesiosoma Californiense}). The body is ovate,
      blackish above, blue or gray below. Called also
      {medialuna}.
      
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Ravelin \Rave"lin\ (r[a^]v"l[i^]n; 277), n. [F.; cf. Sp.
   rebellin, It. revellino, rivellino; perhaps fr. L. re- again
   + vallum wall.] (Fort.)
   A detached work with two embankments which make a salient
   angle. It is raised before the curtain on the counterscarp of
   the place. Formerly called {demilune} and {half-moon}.
   
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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