pilot whale

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any of several large, usually black dolphins of the genus Globicephala, having an outward-curving globular forehead and noted for their occasional mass strandings. Also called blackfish, pothead whale.

Century Dictionary and Cyclopedia

1. n. Same as caaing-whale.

Wiktionary

1. n. Either of two species of whale in the genus Globicephala, dark grey in colour.

GNU Webster's 1913

1. n. (Zoöl.) Same as Blackfish, 1.

WordNet 3.0

1. n. small dark-colored whale of the Atlantic coast of the United States; the largest male acts as pilot or leader for the school