ˈslap-backU.S. Also slapback. [f. slap v.1 + back adv.] A counter-attack, retaliation. 1931Sun (Baltimore) 31 Mar. 10/7 The working of Canada's tariff slap-back against our beloved Smoot-Hawley law.1941New Yorker 27 Dec. 37/1 A resounding Allied slapback at the enemy in the Pacific.