isid·i·um | \īˈsidēəm\
plural isidia\-ēə \

Definition of isidium 

: an outgrowth from the surface of the thallus in certain lichens that resembles a soredium

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 isidium

New Latin, from Isidium, supposed genus of lichens, irregular from Isis genus of gorgonians + Greek eidos form; from the resemblance of lichens that have isidia to gorgonians

Keep scrolling for more

Learn More about isidium

Statistics for isidium

Look-up Popularity

Comments on isidium

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


exaggeratedly or childishly emotional

Get Word of the Day daily email!

Test Your Vocabulary

Words from Greek and Roman Mythology Quiz

  • the-triumph-of-venus-by-alessandro-magnasco
  • Boreal comes from the name of the ancient Greek god of which wind?
True or False

Test your knowledge - and maybe learn something along the way.

Word Winder's CrossWinder

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!