The Collaborative International Dictionary of English v.0.48:

Calcar \Cal"car\, n.; L. pl. Calcaria. [L., a spur, as worn on
   the heel, also the spur of a cock, fr. calx, calcis, the
   heel.]
   1. (Bot.) A hollow tube or spur at the base of a petal or
      corolla.
      [1913 Webster]

   2. (Zool.) A slender bony process from the ankle joint of
      bats, which helps to support the posterior part of the
      web, in flight.
      [1913 Webster]

   3. (Anat.)
      (a) A spur, or spurlike prominence.
      (b) A curved ridge in the floor of the leteral ventricle
          of the brain; the calcar avis, hippocampus minor, or
          ergot.
          [1913 Webster] Calcarate