Etiological is about the cause of a disease, or about the science that looks for that cause. An etiological factor is something that helps bring the illness on; etiological research asks why it started. Doctors and scientists use it; it is not a kitchen-table word. This is the usual American spelling. British English often writes aetiological with ae- — same word, not a different one. Though actually, outside medicine you may also meet etiological myth, a story told to explain why something in the world is the way it is; the core learner sense, though, is medical: cause, or the study of cause.

病因的；病因學的（美式拼法；英式常作 aetiological，同一個字。）