General opposites:
* Known
* Identified
* Determined
* Ascertained
* Understood
More specific opposites, depending on the context:
* Congenital: If talking about the cause of a disease, "congenital" means it's present at birth, while "idiopathic" implies an unknown cause.
* Acquired: If talking about the cause of a condition, "acquired" means it was gained later in life, while "idiopathic" means the cause is unknown.
* Genetic: If talking about the cause of a condition, "genetic" implies a known genetic origin, while "idiopathic" means the cause is unknown.
Example:
* Idiopathic: "The doctor said her condition was idiopathic, meaning they don't know what caused it."
* Opposite: "The patient's illness was determined to be caused by a bacterial infection."
Ultimately, the best opposite for "idiopathic" depends on the specific context and what you want to emphasize.