mackerel shark

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any of various sharks of the family Lamnidae, including the great white shark, mako, and porbeagle, having a pointed snout, a nearly symmetrical tail, and a reputation for aggressiveness.

Century Dictionary and Cyclopedia

1. n. One of several kinds of sharks, as Isurus dekayi, or the porbeagle, Lamna cornubica. They have a forked tail like a mackerel, attain a length of l0 feet, and annoy fishermen by biting off their lines. See porbeagle.

Wiktionary

1. n. Any shark of the order Lamniformes, having two dorsal fins an anal fin, five gill slits and eyes without nictitating membrane

GNU Webster's 1913

1. n. (Zoöl.) the porbeagle.

WordNet 3.0

1. n. fierce pelagic and oceanic sharks