After the argument got heated, he quietly withdrew from the discussion.

withdrew 是动词 withdraw 的过去式。withdraw 由前缀 with-（表示"向后、离开"）和动词 draw（拉、拖）组成，字面意思是"向后拉"，引申为"退出、撤回"的意思。withdrew 在这里表示"从讨论中退出"的动作。