Which term describes a condition that develops without a known cause?

The term that describes a condition which develops without a known cause is idiopathic disease. "Idiopathic" is derived from the Greek words "idios," meaning private or distinct, and "pathos," meaning suffering or disease. In medical terminology, when a disease or condition is classified as idiopathic, it indicates that the underlying cause is not identifiable despite thorough investigation.

Other terms in the list have specific meanings that do not align with the concept of an unknown cause. Hematoma refers to a localized collection of blood outside of blood vessels, usually due to trauma. Hemophilia is a genetic disorder that affects the blood's ability to clot due to deficiencies in certain clotting factors. Immunodeficiency refers to a condition where the immune system's ability to fight infections is compromised or entirely absent, often due to specific known causes such as genetic defects or infections like HIV.

Thus, idiopathic disease is uniquely characterized by the absence of a defined etiology, accurately capturing the concept of a condition arising without a known reason.