pi·ac·u·lar (p?-?k?y?-l?r)adj.1. Making expiation or atonement for a sacrilege: piacular sacrifice.2. Requiring expiation; wicked or blameworthy.[Latin pi?cul?ris, from pi?culum, propitiatory sacrifice, from pi?re, to appease, from pius, dutiful.]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.piacular (pa??ækj?l?) adj1. (Ecclesiastical Terms) making expiation for a sacrilege2. (Ecclesiastical Terms) requiring expiation[C17: from Latin pi?culum propitiatory sacrifice, from pi?re to appease]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014