The Collaborative International Dictionary of English v.0.48:

oldwife \oldwife\ n.
   1. (Zool.) The local name of various fishes, as the European
      black sea bream (Cantharus lineatus), the American
      alewife, etc.
      [WordNet 1.5]

   2. (Zool.) A tropical Atlantic fish (Bessy cerca). [WordNet
      sense 1]

   Syn: queen triggerfish, Bessy cerca, oldwench, Balistes
        vetula.
        [1913 Webster]

   3. (Zool.) A common long-tailed sea duck (Clangula
      hyemalis) of the northern parts of the US; also called
      old squaw. [WordNet sense 2]

   Syn: old squaw, Clangula hyemalis.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Balistes vetula
    n 1: tropical Atlantic fish [syn: queen triggerfish, Bessy
         cerca, oldwench, oldwife, Balistes vetula]