The Collaborative International Dictionary of English v.0.48:

Malleolus \Mal*le"*o*lus\, n.; pl. Malleoli. [L., dim. of
   malleus hammer.]
   1. (Anat.) A projection at the distal end of each bone of the
      leg at the ankle joint. The malleolus of the tibia is the
      internal projection, that of the fibula the external.
      [1913 Webster]

   2. " A layer, " a shoot partly buried in the ground, and
      there cut halfway through.
      [1913 Webster]