Definition of porpoise
(Entry 1 of 2)
1
: any of a family (Phocoenidae) of small gregarious toothed whales
especially
: a blunt-snouted usually dark gray whale (Phocoena phocoena) of the North Atlantic and North Pacific that typically ranges from 5 to 6 feet (1.5 to 1.8 meters) in length
2
: dolphin sense 1a(1)
—not used technically
Note: While not closely related, porpoises and dolphins share a physical resemblance that often leads to misidentification. Porpoises typically have flat, spade-shaped teeth, triangular dorsal fins, and shortened beaks with relatively small mouths while dolphins have cone-shaped teeth, curved dorsal fins, and elongated beaks with larger mouths.
porpoise
verb
porpoised; porpoising; porpoises
Definition of porpoise (Entry 2 of 2)
1
: to leap or plunge like a porpoise
penguins … porpoise out of the water— David Lewis
2
: to rise and fall repeatedly
Keep scrolling for more
Keep scrolling for more
Test Your Vocabulary
Name that Thing: Flower Edition
-
- Name that flower

Test your visual vocabulary with our 10-question challenge!
TAKE THE QUIZ
Spell words. Make bears.
TAKE THE QUIZLove words? Need even more definitions?
Merriam-Webster unabridged
Words at Play
Ask the Editors
Share porpoise
Time Traveler for porpoise
The first known use of porpoise was in the 14th century
See more words from the same century