e·ti·ol·o·gy also ae·ti·ol·o·gy 
(ē′tē-ŏlə-jē)
(ē′tē-ŏlə-jē)n. pl. e·ti·ol·o·gies also ae·ti·ol·o·gies
1.
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.
[Late Latin aetiologia, from Greek aitiologiā : aitiā, cause + -logiā, -logy.]
e′ti·o·logic (-ə-lŏjĭk), e′ti·o·logi·cal adj.
e′ti·o·logi·cal·ly adv.
e′ti·olo·gist n.