"彻底" 的英文是 "thoroughly"。

"Thoroughly" 是一个形容词，表示 "完全地、十分地"。它来自拉丁语 "thoroug"，意思是 "贯穿、通过"。

例句：

I cleaned the room thoroughly. 我彻底打扫了房间。

She thoroughly enjoyed the party. 她十分喜欢那次聚会。