The Collaborative International Dictionary of English v.0.48:

Cero \Ce"ro\, n. [Corrupt. fr. Sp. sierra saw, sawfish, cero.]
   (Zool.)
   A large and valuable fish of the Mackerel family, of the
   genus Scomberomorus. Two species are found in the West
   Indies and less commonly on the Atlantic coast of the United
   States, -- the common cero (Scomberomorus caballa), called
   also kingfish, and spotted, or king, cero (Scomberomorus
   regalis).
   [1913 Webster]