フィン

noun

swim fin; flipper

Used for diving and swimming fins worn on the feet.

• ダイビングのときはフィンをつける。

  I put on fins when diving.

noun

fin (of a surfboard, aircraft, etc.)

Refers to stabilizing or steering fins on equipment such as surfboards, boats, or aircraft.

• サーフボードのフィンが折おれた。

  The fin of the surfboard broke.