Source : Webster's Revised Unabridged Dictionary (1913)

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

   Note: The name is also applied to related genera; as, the
         dog-headed boa ({Xiphosoma caninum}).

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