I accidentally rear-ended the taxi in front when I failed to brake in time.

rear-ended 是动词短语 rear-end 的过去式形式。rear 指"后部"，end 指"末端"，rear-end 字面意思是"用后部撞击"，在驾驶中指"追尾"，即后车撞上前车的尾部。