Merriam-Webster Logo
SINCE 1828
Menu
×

An Encyclopædia Britannica Company

See What's Trending Now See More Trending Words

anal fin

noun

Definition of anal fin

in fishes
:a median unpaired fin on the lower posterior part of the body behind the vent and sometimes confluent with the caudal fin — see fish illustration

Explore M-W

alt-59e8af1b31525
Trending: NY Times: Trump's Call Ignites 'Imbroglio'
alt-59ea52ed7b96f
Learned Fools: On Names for Students
tycoon
17 English Words that Come From Japanese
video-title-words-of-the-year-1066
Words of the Year: 1066

There's more!

Love words? You must — there are over 200,000 words in our free online dictionary, but you are looking for one that’s only in the Merriam-Webster Unabridged Dictionary.

Start your free trial today and get unlimited access to America's largest dictionary, with:

  • More than 250,000 words that aren't in our free dictionary
  • Expanded definitions, etymologies, and usage notes
  • Advanced search features
  • Ad free!
Already a subscriber? Log in.

First Known Use of anal fin

1769

Seen and Heard

What made you want to look up anal fin? Please tell us where you read or heard it (including the quote, if possible).

show hide

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

WORD OF THE DAY

nuncupative

play

spoken rather than written

Get Word of the Day daily email!

TRENDING NOW

  1. imbroglio "a public scandal"

  2. spurious of a deceitful nature or quality

  3. righteous We provide an assortment of definitions

  4. Kafkaesque 'A nightmarish quality'

  5. mike "microphone"

SEE ALL

BROWSE DICTIONARY

Test Your Vocabulary

The Exceptions Quiz III

  • one-green-toy-robot-amidst-many-red-toy-robots
  • Which of these words does not mean "nonsense"?
How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

TAKE THE QUIZ
SCRABBLE® Sprint

Test Your Knowledge - and learn some interesting things along the way.

TAKE THE QUIZ

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Words at Play

alt-59ea52ed7b96f
Learned Fools: On Names for Students

Where did we get 'freshman' and 'sophomore'?

alt-59e900afadac6
The Synonyms 'Discover' and 'Invent'

In the past, you could invent fruit.

alt-59e8c3440f453
I'll Have the Us(ual)

Shortening 'usual': easy to say, hard to spell

alt-59e77dc36c593
The Origins of 'Lobbyist'

From the front hallways to the back rooms

Ask the Editors

video-title-words-of-the-year-1066
Words of the Year: 1066

Or, Why Pig Meat is Called 'Pork' and Cow Meat is Called 'Beef'

payday
How Often Is 'Biweekly'?

Don't get us started on 'bimonthly'

video-irregardless-grammar-peeve-blend-of-the-synonyms-irrespective-and-regardless
Irregardless

It is in fact a real word (but that doesn't mean you should use it).

video-moose-goose-weird-plurals
Weird Plurals

One goose, two geese. One moose, two... moose. What's up with that?

Word Games

one-green-toy-robot-amidst-many-red-toy-robots
The Exceptions Quiz III

Which of these things doesn't belong?

Take the quiz
knupfer-painting-solon-before-croesus
Forms of Government Quiz

Name that government! Or something like that.

Take the quiz
How Strong Is Your Vocabulary?
How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

Take the quiz
SCRABBLE® Sprint
SCRABBLE® Sprint

SCRABBLE® fans, sharpen your skills!

Play the game