cal·ci·tri·ol (k?l?s?-tr??ôl?, -?l?)n. The active metabolite of vitamin D, C27H44O3, that is synthesized in the kidneys and liver from vitamin D2 or vitamin D3 and acts as a calcium-regulating hormone. A synthetic form is used as a drug to treat hypocalcemia, bone disease caused by renal failure, and, in topical preparations, psoriasis.[calci- + triol.]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.