fin

1 of 4

noun (1)

ˈfin 

1

: an external membranous process of an aquatic animal (such as a fish) used in propelling or guiding the body see fish illustration

2

: something resembling a fin: such as

a

: hand, arm

b(1)

: an appendage of a boat (such as a submarine)

(2)

: an airfoil attached to an airplane for directional stability

c

: flipper sense 1b

d

: any of the projecting ribs on a radiator or an engine cylinder

finlike

ˈfin-ˌlīk 

adjective

fin

2 of 4

verb

finned; finning

transitive verb

: to equip with fins

intransitive verb

1

: to show the fins above the water

2

: to move through water propelled by fins

fin

3 of 4

noun (2)

slang

: a 5-dollar bill

fin

4 of 4

abbreviation

1

finance; financial

2

finish

Examples of fin in a Sentence

Recent Examples on the Web

Noun

The robot’s fins flap in response to external magnetic fields, enabling it to swim, make sharp 90-degree turns, and navigate complex trajectories, all while transmitting real-time data to a digital twin. —Neetika Walter, Interesting Engineering, 26 Nov. 2025

The kit adds a revised underbody, tweaks to the front spoiler (and extended lip) and rear diffuser (longer fins), and an even larger rear wing with a Gurney flap. —Bryan Hood, Robb Report, 24 Nov. 2025

Verb

The cruel and wasteful practice of shark finning − cutting off fins and discarding the still-living animals back into the sea − pushes shark populations towards the brink of extinction and jeopardizes marine ecosystems. —Natalie Neysa Alund, USA Today, 21 Nov. 2025

There are no dolphins hanging around the buoy at Grace Bay today, just me, bobbing like a cork, mask, weight belt, and fins on, watching schools of fish zigzag beneath the surface. —Vanita Salisbury, AFAR Media, 6 Nov. 2025

Word History

Etymology

Noun (1)

Middle English finn, from Old English

Noun (2)

Yiddish finf five, from Middle High German, from Old High German — more at five

First Known Use

Noun (1)

before the 12th century, in the meaning defined at sense 1

Verb

1861, in the meaning defined at intransitive sense 2

Noun (2)

1916, in the meaning defined above

Phrases Containing fin

• dorsal fin
• fin de siècle
• fin whale
• lobe-fin
• pectoral fin
• pelvic fin
• swim fin
• tail fin

Rhymes for fin

• been
• bin
• chin
• din
• djinn
• finn
• gin
• grin
• in
• kin
• linn
• linne

Kids Definition

fin

noun

ˈfin

1

: a thin process on the outside of an aquatic animal (as a fish or whale) used in propelling or guiding the body

2

: something shaped like a fin

finlike

-ˌlīk

adjective

finned

ˈfind

adjective