After a war, a storm, a crash, or a big public fight, the trouble does not stop at once. Buildings are broken, people are hurt, and someone still has to clean up, pay, and live with what happened. That stretch of time — and the mess you are still dealing with — is the aftermath. News writers use it a lot: in the aftermath of the earthquake. It almost always follows something bad, or at least something very big; you would not normally talk about the aftermath of a birthday party. Though actually, the first half is easy (after), but the second half is an old farming word. Math here meant a cutting of grass. An aftermath was once the new grass that grew after the farmer had already cut the field. Today almost nobody uses that farm meaning; we keep the picture of what grows after the cutting, and we use it for results.