Source : Webster's Revised Unabridged Dictionary (1913)

Sulcus \Sul"cus\, n.; pl. {Sulci}. [L., a furrow.]
   A furrow; a groove; a fissure.

Source : WordNet®

sulcus
     n : (anatomy) any of the narrow grooves in an organ or tissue
         especially those that mark the convolutions on the
         surface of the brain
     [also: {sulci} (pl)]