The Collaborative International Dictionary of English v.0.48:

Boa \Bo"a\ (b[=o]"[.a]), n.; pl. Boas. [L. boa a kind of water
   serpent. Perh. fr. bos an ox.]
   1. (Zool.) A genus of large American serpents, including the
      boa constrictor, the emperor boa of Mexico (Boa
      imperator), and the chevalier boa of Peru (Boa eques).
      [1913 Webster]

   Note: The name is also applied to related genera; as, the
         dog-headed boa (Xiphosoma caninum).
         [1913 Webster]

   2. A long, round fur tippet; -- so called from its
      resemblance in shape to the boa constrictor.
      [1913 Webster]