"hoist by one’s own petard"
The New Dictionary of Cultural Literacy, Third Edition. 2002.
hoist by one’s own petard
(pi-TAHRD) To be caught in one’s own trap: “The swindler cheated himself out of most of his money, and his victims were satisfied to see him hoist by his own petard.” A “petard” was an explosive device used in medieval warfare. To be hoisted, or lifted, by a petard literally means to be blown up.
The New Dictionary of Cultural Literacy, Third Edition. Edited by E.D. Hirsch, Jr., Joseph F. Kett, and James Trefil. Copyright © 2002 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.