anaconda

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of several nonvenomous, semiaquatic snakes of the genus Eunectes of tropical South America that kill by coiling around their prey, especially E. murinus, which can attain a length of up to 9 meters (29.5 feet).

from The Century Dictionary.

• noun A very large serpent of Ceylon, a kind of python, variously identified as Python reticulatus, or P. molurus, or P. tigris; hence, some Indian species of that genus. Also called pimbeva and rock-snake.
• noun Used mistakenly by Daudin as the specific name of a large serpent of South America, Boa murina (Linnæus), B. anacondo (Daudin), now generally known as Eunectes marinus; hence, some large South American boa, python, or rock-snake. In zoology the name is becoming limited to the Eunectes murinus.
• noun In popular language, any enormous serpent which is not venomous, but which envelops and crushes its prey in its folds; any of the numerous species of the families Boidæ and Pythonidæ; any boa constrictor.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) A large South American snake of the Boa family (Eunectes murinus), which lives near rivers, and preys on birds and small mammals. The name is also applied to a similar large serpent (Python tigris) of Ceylon.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any of various large nonvenomous snakes of the genus Eunectes, found mainly in northern South America. Their length can grow to as much as 5 m (15 ft).
• noun by extension, slang, vulgar Penis.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun large arboreal boa of tropical South America