When I asked him why he was late, his quick rejoinder was that the traffic was terrible.

rejoinder 是名词，来自动词 rejoin（回答、回应），由前缀 re-（表示"再次"）和 join（加入、连接）组成。rejoinder 指"迅速的回答或反驳"，通常用于对话中一方对另一方的回应。