A depression or hollow resembling or suggesting a valley, as the point at which the two slopes of a roof meet.
屋谷与山谷相象或让人想起山谷的凹处或洼处，如屋顶两个斜面相遇的那一点
His protests on human rights sound hollow.
他就人权问题提出的抗议听来很空洞。
This tree looks high and strong but actually its trunk is hollow.
这棵树看起来又高又壮，实际上树干是空的。
