To stop crying; to cease crying (often after calming down or crying something out). Intransitive.
赤ちゃんがミルクを飲んだら、すぐに泣き止んだ。
The baby stopped crying as soon as he drank the milk.
彼女は映画を見て泣いたが、エンドロールが始まるころには泣き止んでいた。
She cried while watching the movie, but had stopped crying by the time the end credits rolled.
先生の冗談で子どもたちが泣き止んだ。
The teacher's joke made the children stop crying.