# fin

/ˈfɪn/ (US) · /fˈɪn/ (UK)

Source: https://englishreference.com/word/fin
Updated: 2026-06-20

## Senses

### 1. on a fish

noun · CEFR A2

a thin, flat part that sticks out from the body of a fish to help it swim and balance.

For teachers: an organ of a fish or cetacean used for propulsion, steering, or balancing in water.

- The shark's dorsal fin appeared above the water as it swam near the boat.
- Marine biologists can often identify individual whales by the unique notches and scars found on their dorsal fins.

### 2. swimming equipment

noun · CEFR B1

a long, flat rubber shoe that you wear to swim faster underwater.

For teachers: a flipper-like device worn on the feet to increase propulsion while swimming or diving.

- You should wear fins and a mask if you want to go snorkeling.
- The diver kicked his fins powerfully to reach the coral reef before the current shifted.

### 3. aerospace/mechanical

noun · CEFR B2 · Technical

a flat part on a plane, rocket, or machine that helps it stay steady or cool down.

For teachers: a fixed or adjustable vane used for aerodynamic stability or to increase the surface area for heat dissipation.

- The small fins on the back of the rocket help it fly straight.
- The engine's cooling fins were clogged with dust, causing the internal temperature to rise dangerously during the long flight.

### 4. five-pound note

noun · CEFR C1 · Slang · British English · American English

a slang word for a five-pound note or five dollars.

For teachers: a slang term for a five-unit currency note, specifically five pounds in the UK or five dollars in the US.

- He handed the shopkeeper a fin to pay for the magazine.
- In the old detective novel, the protagonist slipped the informant a fin in exchange for the address of the warehouse.

### 5. to remove fins

verb · CEFR C1 · Technical

to cut the fins off a fish, especially a shark.

For teachers: to remove the fins from a fish, often used in the context of the controversial practice of shark finning.

- Many countries have banned the practice of finning sharks at sea.
- The environmental agency reported that thousands of sharks are illegally finned every year to satisfy the demand for specialty soups.

## Examples

- The shark's fin appeared above the water.
- Divers identified the species of the whale by the unique shape and scarring on its dorsal fin.
- Engineers designed the rocket's stabilizing fins to ensure a vertical trajectory, mimicking the way a fish uses its anatomy to maintain orientation against a current.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.