Finned describes something that has fins: the flat, winglike parts that help fish, whales, and some other water animals steer and move through water. A shark's dorsal fin cuts through the surface as it swims, and its other fins help it turn quickly. Dolphins are finned mammals that use their fins to glide gracefully through the ocean.

The word can describe real animals or things designed to look or work like them. Engineers design finned rockets and missiles because fins help stabilize them in flight, just like they help fish stay balanced in water. Old cars from the 1950s often had dramatic finned designs on their rear ends, with metal shaped to look like shark fins. Scuba divers wear finned flippers on their feet to swim more powerfully underwater.

Sometimes people use finned poetically to describe the water creatures themselves: “finned predators” sounds more dramatic than just saying “fish.” The word emphasizes that special feature that makes underwater animals so different from land creatures like us.