1、roof英[ruːf]美[ruːf]，n.顶部; 屋顶; 车顶; 有…顶的; 洞顶; 隧道顶; 口腔顶部;vt.给…盖顶; 盖上屋顶。

2、[例句]The limestone is sufficiently fissured for tree roots to have breached the roof of the cave.石灰岩上有许多缝隙，故而树根能从岩洞顶部长出来。