thresher shark

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

• noun Any of various large sharks of the genus Alopias, especially A. vulpinus of warm and temperate waters worldwide, having a tail with a long whiplike upper lobe with which it strikes the surface of the water.

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

• noun Any of three species of sharks, in the genus Alopias.

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

• noun large pelagic shark of warm seas with a whiplike tail used to round up small fish on which to feed