Source : Webster's Revised Unabridged Dictionary (1913)

Fossa \Fos"sa\, n.; pl. {Foss[AE]}. [L., a ditch. See {Fosse}.]
   (Anat.)
   A pit, groove, cavity, or depression, of greater or less
   depth; as, the temporal fossa on the side of the skull; the
   nasal foss[ae] containing the nostrils in most birds.

Source : WordNet®

fossa
     n 1: a concavity in a surface (especially an anatomical
          depression) [syn: {pit}]
     2: monotypic genus of Madagascar civets closely related to palm
        civets [syn: {genus Fossa}]
     3: largest carnivore of Madagascar; intermediate in some
        respects between cats and civets [syn: {fossa cat}, {Cryptoprocta
        ferox}]
     [also: {fossae} (pl)]

fossae
     See {fossa}