anaconda: [18] 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. [anaconda etymology, anaconda origin, 英语词源]