n. [ Gr. &unr_;, &unr_;, ray + -logy. ] The science which treats of rays of light, especially of the actinic or chemical rays. [ 1913 Webster ]

n. [ L. aetologia, Gr. a'itiologi`a; a'iti`a cause + lo`gos description: cf. F. étiologie. ] 1. The science, doctrine, or demonstration of causes; esp., the investigation of the causes of any disease; the science of the origin and development of things; etiology. AS [ 1913 Webster ]

2. The assignment of a cause. [ 1913 Webster ]

3. (Med.) The cause or origin of a disease. Now more commonly written etiology. [ PJC + AS ]