Flat, fin-like limbs used by sea creatures like seals and penguins to swim; also rubber fins worn by divers.
From 'flip' (Middle English, possibly imitating the sound), plus '-er' making it a noun. The word originally described the action of flipping or fluttering, then the body part that performs that action.
Flippers are a perfect example of convergent evolution—seals, penguins, dolphins, and sea turtles all evolved flippers independently because 'flat paddle-shaped limbs' is the best design for swimming through water.
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