WordNet sense 1 (small dark-colored whale of the Atlantic coast of the United States; the largest male acts as pilot or leader for the school):

blackfish, pilot whale, common blackfish, Globicephala melaena

WordNet sense 2 (large whale with a large cavity in the head containing spermaceti and oil; also a source of ambergris):

cachalot, sperm whale, Physeter catodon