Merriam-Webster Logo
SINCE 1828
Menu
dictionary thesaurus

Pennales

plural noun
Pen·​na·​les | \ pəˈnā(ˌ)lēz\

Definition of Pennales

: an order of diatoms having a raphe or pseudoraphe and ornamentation of the valves always bilaterally arranged in relation to a line rather than to a point — compare centrales

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!

History and Etymology for Pennales

New Latin, from Latin penna feather + New Latin -ales

Keep scrolling for more

Learn More about Pennales

Statistics for Pennales

Look-up Popularity

Comments on Pennales

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

Show Comments  Hide Comments 

WORD OF THE DAY

inexorable

Listen to the pronounciation of inexorable

not to be persuaded, moved, or stopped

Get Word of the Day daily email!

Test Your Vocabulary

Words from Greek and Latin Quiz

  • roman forum
  • Which of the following months comes from a Latin word for “ten”?
Name That Thing

Test your visual vocabulary with our 10-question challenge!

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
Ask the Editors
Word Games