Source : Webster's Revised Unabridged Dictionary (1913)

Cisco \Cis"co\, n. (Zo["o]l.)
   The Lake herring ({Coregonus Artedi}), valuable food fish of
   the Great Lakes of North America. The name is also applied to
   {C. Hoyi}, a related species of Lake Michigan.

Source : WordNet®

cisco
     n 1: cold-water fish caught in Lake Superior and northward [syn:
          {lake herring}]
     2: important food fish of cold deep lakes of North America
        [syn: {lake herring}, {Coregonus artedi}]
     [also: {ciscoes} (pl)]