What term describes a condition of unknown cause?

The term "idiopathic" specifically refers to a disease or condition for which the cause is not known. This term is derived from the Greek roots "idio," meaning "personal," and "pathos," meaning "suffering" or "disease," thus suggesting that the condition arises spontaneously without any identifiable cause.

For instance, idiopathic conditions can include diseases like idiopathic pulmonary fibrosis, where despite extensive testing, the exact cause of the disease remains elusive. Medical terminology frequently utilizes this term to categorize cases that present symptoms or abnormalities without a clear underlying etiology.

In contrast, "nosomial" refers to infections acquired in a hospital setting, which clearly indicates a known origin—hospitalized environments. A "syndrome" is a collection of signs and symptoms that occur together and are indicative of a particular disease or condition but does not signify an unknown cause. "Atresia" describes a congenital condition where a body orifice or passage is absent or closed, implying a specific developmental anomaly rather than an unidentified cause.

Thus, the correct answer, "idiopathic," is the term that directly conveys the concept of a condition arising without a known cause, making it the most accurate choice.