e·ti·ol·o·gy also ae·ti·ol·o·gy (??t?-?l??-j?)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 aitiologi? : aiti?, cause + -logi?, -logy.]e?ti·o·log?ic (-?-l?j??k), e?ti·o·log?i·cal adj.e?ti·o·log?i·cal·ly adv.e?ti·ol?o·gist n.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.etiology (?i?t???l?d??) n, pl -gies a variant spelling of aetiology etiological, etiologic adj ?etio?logically adv ?eti?ologist nCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014e?ti?ol?o?gy (?i ti??l ? d?i) n., pl. -gies. 1. a. the study of the causes of diseases. b. the cause or origin of a disease. 2. a. any study of causes, causation, or causality. b. the cause postulated for something. [1545?55;