Idiopathic
Etymology
From Greek idios, "one’s own, private, peculiar" (the root of "idiom" and "idiosyncrasy"), plus pathos, "disease." Together they suggest a disease that is a law unto itself — self-arising. In practice "idiopathic" is the label doctors use when every known cause has been ruled out. It sounds like an explanation but really marks the edge of current knowledge.
adjective · /id-ee-oh-PATH-ik/
Describing a disease that arises on its own, with no identifiable cause.
What it names
The honest medical admission hidden inside a technical word — "we can see it, but we don’t know why it happened."
Example
After every test came back normal, the tremor was classed as idiopathic.
Related idea
Iatrogenic names a clear cause — the treatment itself; idiopathic means no cause could be found at all.
See also