Source : Webster's Revised Unabridged Dictionary (1913)

Fissure \Fis"sure\, n. [L. fissura, fr. findere, fissum, to
   cleave, split; akin to E. bite: cf. F. fissure.]
   A narrow opening, made by the parting of any substance; a
   cleft; as, the fissure of a rock.

   {Cerebral fissures} (Anat.), the furrows or clefts by which
      the surface of the cerebrum is divided; esp., the furrows
      first formed by the infolding of the whole wall of the
      cerebrum.

   {Fissure needle} (Surg.), a spiral needle for catching
      together the gaping lips of wounds. --Knight.

   {Fissure of rolando} (Anat.), the furrow separating the
      frontal from the parietal lobe in the cerebrum.

   {Fissure of Sylvius} (Anat.), a deep cerebral fissure
      separating the frontal from the temporal lobe. See Illust.
      under {Brain}.

   {Fissure vein} (Mining), a crack in the earth's surface
      filled with mineral matter. --Raymond.

Source : WordNet®

fissure of Sylvius
     n : the deepest and most prominent of the cortical fissures;
         separates the frontal lobes and temporal lobes in both
         hemispheres [syn: {Sylvian fissure}, {lateral cerebral
         sulcus}, {sulcus lateralis cerebri}]