The Collaborative International Dictionary of English v.0.48:

Lune \Lune\ (l[=u]n), n. [L. luna moon: cf. F. lune. See
   Luna.]
   1. Anything in the shape of a half moon. [R.]
      [1913 Webster]

   2. (Geom.) A figure in the form of a crescent, bounded by two
      intersecting arcs of circles.
      [1913 Webster]

   3. A fit of lunacy or madness; a period of frenzy; a crazy or
      unreasonable freak. [Obs.]
      [1913 Webster]

            These dangerous, unsafe lunes i' the king. --Shak.
      [1913 Webster]