The Collaborative International Dictionary of English v.0.48:

Scoter \Sco"ter\, n. [Cf. Prov. E. scote to plow up.] (Zool.)
   Any one of several species of northern sea ducks of the genus
   Oidemia.
   [1913 Webster]

   Note: The European scoters are Oidemia nigra, called also
         black duck, black diver, surf duck; and the
         velvet, or double, scoter (Oidemia fusca). The common
         American species are the velvet, or white-winged,
         scoter (Oidemia Deglandi), called also velvet duck,
         white-wing, bull coot, white-winged coot; the
         black scoter (Oidemia Americana), called also black
         coot, butterbill, coppernose; and the surf scoter,
         or surf duck (Oidemia perspicillata), called also
         baldpate, skunkhead, horsehead, patchhead,
         pishaug, and spectacled coot. These birds are
         collectively called also coots. The females and young
         are called gray coots, and brown coots.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Horsehead \Horse"head`\, n. (Zool.)
   The silver moonfish (Selene vomer).
   [1913 Webster]

WordNet (r) 3.0 (2006):

horse-head
    n 1: any of several silvery marine fishes with very flat bodies
         [syn: moonfish, Atlantic moonfish, horsefish,
         horsehead, horse-head, dollarfish, Selene
         setapinnis]