also ae·ti·ol·o·gy (ē′tē-ŏl′ə-jē)

n. pl. e·ti·ol·o·gies also ae·ti·ol·o·gies1.

a. The study of causes or origins.  b. The branch of medicine that deals with the causes or origins of disease.

2. a. Assignment of a cause, an origin, or a reason for something. b. The cause or origin of a disease or

disorder as determined by medical diagnosis. 

I doubt seriously whether there is a more humiliating moment in the life of a medical man, either as teacher or practitioner, than when asked by a student or patient, “What is the cause of this?” and he is forced to say, “I do not know.
— MARCUS HAASE, M.D., "ETIOLOGY UNKNOWN", The Journal of the American Medical Association, September 1, 1923