grampus (n.)

a word applied to killer whales and other large, dolphin-like creatures, 1590s, earlier graundepose (1520s), altered (by influence of grand) from Middle English graspeys (late 13c.), from Anglo-French grampais, from Old French graspois, craspois "whale, (salted) whale meat; blubber; seal," from Medieval Latin craspicis, literally "great fish" or "fat fish," from Latin crassus "thick" (which is of unknown origin) + piscis "fish" (from PIE root *pisk- "a fish"). For specifics of usage in English, see OED.