一个主意an idea
个好主意 A Good Idea
idea既是可数名词（C）,也是不可数名词（U）,不同意思有不同的属性.
1、主意;打算;计划[C][(+of)][+to-v][+that]
He hit upon the good idea of spending the weekend in the nearby holiday camp.
他想到去附近度假营过周末这个好主意.
2、构想;概念[C][U][(+of)]
Have you any idea of what he is up to?
你知道他想干什么吗?
3、了解,明白[C][(+of)][+wh-]
I have no idea what to do.
我不知道该怎么办.
4、臆测;推量[C][+(that)]
I've an idea that he'll soon quit the job.
我猜想他不久就要辞掉这工作.
5、意见,见解;信念[(+about/on)][+that]
That at least is my idea about friendship.
至少那是我对友谊的理解.
6、思想;观念[C][U]
He destroyed feudal ideas in literature.
他摧毁了文学中的封建思想.