what('s) an idea!

Today in English, we had a review of nouns.  I was trying to explain that a noun can be an idea, which is a hard concept to teach.  I did my best.  It came out a little something like this: "A noun can be an idea.  An idea is something that you can think about, but you can't see it or touch it...like friendship or love."  I'm not quite sure I got the point across.  Immediately after my oh-so-precise explanation, Roger (you may remember him from the spelling quiz) said, "Oh, like my nose!  I can think about it, but I can't put my fingers in it!"