n.空白；空隙；腔隙

Fill up a lacuna in one's knowledge 填补知识上的空白。

His long reticence temporarily distracted attention from a bigger lacuna. 他始终保持沉默，分散了人们对一个更大缺漏的注意力。

There was so much very deep lacuna in his crude big hands. 粗糙的大手上一道道很深的裂口。