constrictor

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

• noun One that constricts, as a muscle that contracts or compresses a part or organ of the body.
• noun Any of various snakes, such as the python or boa, that tightly coil around and asphyxiate their prey.

from The Century Dictionary.

• noun That which constricts, contracts, or draws together; specifically, in anatomy, a muscle which draws parts together, or closes an opening; a sphincter: as, the constrictor of the esophagus.
• noun A large serpent which envelops and crushes its prey in its folds: as, the boa-constrictor. See boa.
• noun The technical specific name of the common black-snake of North America, Bascanion constrictor. See cut under black-snake.
• Acting as a constrictor; constricting: as, a constrictor muscle.

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

• noun That which constricts, draws together, or contracts.
• noun (Anat.) A muscle which contracts or closes an orifice, or which compresses an organ; a sphincter.
• noun (Zoöl.) A serpent that kills its prey by inclosing and crushing it with its folds.

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

• noun That which constricts or tightens.

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

• noun any of various large nonvenomous snakes that kill their prey by crushing it in its coils