plural noun
Ac·​an·​tho·​dii | \ ˌaˌkanˈthōdēˌī, ˌakən- \

Definition of Acanthodii

: a subclass of Placodermi comprising primitive Paleozoic fishes having the anterior margin of each fin supported by a stout spine and often having one or more pairs of spines similar to the fin spines along the lower lateral part of the body between the paired fins of each side

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!

First Known Use of Acanthodii

1851, in the meaning defined above

History and Etymology for Acanthodii

New Latin, from Acanthodes

Keep scrolling for more

Learn More about Acanthodii

Time Traveler for Acanthodii

Time Traveler

The first known use of Acanthodii was in 1851

See more words from the same year

Statistics for Acanthodii

Cite this Entry

“Acanthodii.” The Dictionary, Merriam-Webster Inc., Accessed 23 January 2020.

Comments on Acanthodii

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


out of the ordinary or unreasonable

Get Word of the Day daily email!

Test Your Vocabulary

Intact Latin Quiz

  • roman tablet
  • What did focus mean in Latin?
Spell It

Can you spell these 10 commonly misspelled words?

Add Diction

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

Love words? Need even more definitions?

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