1 [I,T] to know or realize the meaning of sth 明白；理解: I'm not sure that I really understand. 我不肯定自己是否真的明白。I didn't understand the instructions. 我不明白那些指示。Please speak more slowly. I can't understand you. 请说得慢一点，我听不明白。Do you understand what I'm asking you? 你明白我在问你什么吗？

2 [T] to know how or why sth happens or why it is important 了解，理解（原因、情况或重要性）: I can't understand why the engine won't start. 我不知道发动机为什么开不动。As far as I understand it, the changes won't affect us. 据我所知，这些改变不会影响我们。

3 [T] to know sb's character and why he/she behaves in a particular way 体谅；谅解: It's easy to understand why she felt so angry. 她那样生气，原因很易理解。

4 [T] (formal 正式) to have heard or been told sth 听说；得知；获悉