Definition of "idiopathic" [id•i•o•path•ic]

• Of, relating to, or designating a disease having no known cause. (adjective)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The word idiopathic in idiopathic pulmonary fibrosis means no one knows what causes the disease."
• "Annoyingly for some people, no actual cause can be found - this is known as idiopathic rhinitis and is more difficult to treat."
• "Medically, it is 'idiopathic' - which means that it arises spontaneously, from an unknown cause."