1. the flat parts that stick out from a fish’s body and help it swim
2. rubber attachments worn on the feet to help swim faster
3. flat projections on aircraft, rockets, or vehicles for stability or control
Usage: technical

Examples

• The shark’s dorsal fin cut through the water.
• Fish use their fins to steer and balance while swimming.
• She put on her fins before diving into the pool.
• The scuba divers wore masks and fins.
• The rocket had four fins at its base for stability.
• The surfboard had three fins attached to the bottom.