re·tor·sion or re·tor·tion (rĭ-tôr'shən) n. An act perpetrated by one nation upon another in retaliation or reprisal for a similar act perpetrated by the other nation.
[Probably French rétorsion, from Latin retortus (influenced by Late Latin torsiō, a twisting, wringing), past participle of retorquēre, to cast back; see retort1.]