Try to define time. Or just go to the wikipedia article and listen to them try to define it, and digress into a discussion on how some people don't believe in it.

It's very hard to describe time without using the word time: A series of events -- What's an event? The best one I have is: Why can't two object occupy the same space? Well, they can, but at different times. Not really an explanation, but I think it's a good illustration.

Isn't time sort of like goodness, so fundamental that it's indescribable with invoking itself?