1. 洞向地表開有出口的地下的或通向地內的中空或天然的通道
   A hollow or natural passage under or into the earth with an opening to the surface.
2. 角狀物天然的或合成的，類似于角質物的物質
   A natural or synthetic substance resembling this material.
3. 鉆石小的天然的或人造寶石，用作手表中的軸承
   A small natural or artificial gem used as a bearing in a watch.
4. 有些昆蟲有一種天然的保護色可以防止敵人的襲擊。
   Some insect have a natural camouflage which hide them from the attack of their enemy.

天的英語翻譯：

然的英語翻譯：