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.