The Collaborative International Dictionary of English v.0.48:

Armil \Ar"mil\, n. [L. armilla a bracelet, fr. armus arm: cf.
   OF. armille.]
   1. A bracelet. [Obs.]
      [1913 Webster]

   2. An ancient astronomical instrument.
      [1913 Webster]

   Note: When composed of one ring placed in the plane of the
         equator for determining the time of the equinoxes, it
         is called an equinoctial armil; when of two or more
         rings, one in the plane of the meridian, for observing
         the solstices, it is called a solstitial armil.
         --Whewell.
         [1913 Webster]