noun isid·i·um \īˈsidēəm\

Definition of isidium



  1. :  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.

Join MWU now and get access to America’s largest dictionary, with:

  • 300,000 words that aren't in our free dictionary
  • Expanded definitions, etymologies, and usage notes
  • Advanced search features
  • Ad free!

Origin and Etymology of 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 — more at idol

Seen and Heard

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


to criticize severely

Get Word of the Day daily email!