porpoise

Etymology

From Middle English porpeys, purpeys, borrowed from Anglo-Norman porpeis, purpeis, Old French pourpois, porpois, pourpais, porpeis (“porpoise”), from Vulgar Latin *porcopiscis (“porpoise”, literally “pig-fish”), from Latin porcus (“pig”) + piscis (“fish”). Compare (in transposed order) obsolete Italian pesce porco and Portuguese peixe porco; also Latin porcus marinus (“sea hog”), akin in formation to German Meerschwein, English mereswine. More at mereswine.

noun

1. A small cetacean of the family Phocoenidae, related to dolphins and whales.
   They captured 25 porpoises and set them free back into the Yangtze after raising them for a month in Puqi County, Hubei. 1991, Kaiya Zhou, Zhang Xingduan, translated by Luo Changyan, Baiji: The Yangtze River Dolphin and Other Endangered Animals of China, →LCCN, →OCLC, page 76
2. (Canada, US, imprecisely) Any small dolphin.

verb

1. (intransitive) Said of an air-breathing aquatic animal such as a porpoise or penguin: To repeatedly jump out of the water to take a breath and dive back in a continuous motion.
   Urging them to join me, I raced in circles through the surging water, chased my tail for the children, blew spouts of foam through the sunfilled spray, porpoised to and fro across the river in shallow leaps that stitched the air and water into a table-lace of foam. 1979, J.G. Ballard, The Unlimited Dream Company, chapter 15
2. (intransitive) Said of an aircraft: to make a series of plunges when taking off or landing; or of a watercraft: to successively plunge up and down in the water.