fin
nounUK /fɪn/
US /fɪn/
A fin is a flat part on a fish that helps it swim.
The fish used its tail fin to swim away quickly.
OTHER MEANINGS
2. A thin upright part on a car, boat, or airplane that helps keep it steady.
The old car had big fins on the back.
3. A rubber flipper worn on the foot for swimming.
She put on her fins before diving into the water.
4. A small flat piece sticking out from a machine that helps cool it.
The engine has metal fins to let heat escape.