dorsal fin

American  

noun

1. the fin or finlike integumentary expansion generally developed on the back of aquatic vertebrates.

---

dorsal fin British  

noun

1. any unpaired median fin on the backs of fishes and some other aquatic vertebrates: maintains balance during locomotion

---

Etymology

Origin of dorsal fin

First recorded in 1760–70

Example Sentences

Winter had put a life vest on the dog resembling a shark, with a dorsal fin protruding from its back.

From Los Angeles Times • Oct. 9, 2024

What they spotted, a whale without a dorsal fin, led the researchers to think that it might be a North Atlantic right whale, a critically endangered species that the aquarium has been closely monitoring.

From New York Times • Mar. 6, 2024

They can be identified by their lack of a dorsal fin and mottled appearance that makes them very different from whales more commonly seen off New England such as the humpback whale and minke whale.

From Seattle Times • Mar. 5, 2024

And unlike other mosasaurs, or large extinct marine reptiles, it had a dorsal fin like a shark's that would have helped it turn quickly and with precision in the water.

From Science Daily • Dec. 12, 2023

I drew a dorsal fin on top and an anal fin on the bottom, to prevent the shark from rolling side to side when it was moving forward.

From "The Line Tender" by Kate Allen