My Lai mas ‧ sa ‧ cre, the /ˌmiː laɪ ˈmæsəkəʳ/ BrE AmE
a village in Vietnam where, in 1968, a group of US soldiers cruelly killed several hundred people, mostly old people, women, and children, during the Vietnam War. The officer who led this attack, Lt William Calley, was later put on trial and sent to prison, but he was allowed to go free after a short time. This event influenced many Americans to oppose the war.