anaconda:  The term anaconda has a confused history. It appears to come from Sinhalese henakandayā, literally ‘lightningstem’, which referred to a type of slender green snake. This was anglicized as anaconda by the British naturalist John Ray, who in a List of Indian serpents 1693 described it as a snake which ‘crushed the limbs of buffaloes and yoke beasts’.
And the 1797 edition of the Encyclopedia Britannica notes it as a ‘very large and terrible snake [from Ceylon] which often devours the unfortunate traveller alive’. However, in the early 19th century the French zoologist François Marie Daudin for no known reason transferred the name to a large South American snake of the boa family, and that application has since stuck.
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 snake name like it now is found 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].