I know the meaning of loneliness. [=I know what it is like to be lonely]我知道孤单的滋味。

Those people don't know the meaning of hard work.那些人不懂得努力工作的意义。

He doesn't know the meaning of fear. [=he is very brave]他不知道什么叫恐惧。

I'll never stop trying. I don't know the meaning of the word “failure.” [=I am determined not to fail]我会一直尝试下去，我不知道什么叫作“失败”。