plac·en·ta·tion (pl?s??n-t??sh?n)n.1. a. Formation of a placenta in the uterus.b. The type or structure of a placenta.2. Botany Arrangement of placentas within the ovary.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.placentation (?plæs?n?te???n) n1. (Botany) botany the way in which ovules are attached in the ovary2. (Zoology) zoology a. the way in which the placenta is attached in the uterusb. the process of formation of the placentaCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014