anaconda n.

1768, a name first used in English to name a Ceylonese python, it was applied erroneously to a large South American boa, called in Brazil sucuriuba. The word is of uncertain origin, and no similar snake name is found now in Sinhalese or Tamil. One suggestion is that it is a Latinization of Sinhalese henacandaya "whip snake," literally "lightning-stem" [Barnhart]. Another suggestion is that it represents Tamil anaikkonda "having killed an elephant" [OED].