Retorsion (French rétorsion, from Latin retortus (influenced by Late Latin, 1585–95, torsi, a twisting, wringing),The American Heritage Dictionary of the English Language, Fourth Edition copyright ?2000 by Houghton Mifflin Company. a phrase used in International Law is an act perpetrated by one nation upon another in retaliation or reprisal for a similar act perpetrated by the other nation.