The S-word

The other day, Natalie told me out of the blue, and in a very serious tone of voice:
"Mommy, I know what the S-word is."
My first thought: Hmm, Okay, then, time to have a discussion about which words are appropriate to use... Let's see where this goes.

Here's the rest of the conversation:
Me: You do?
Natalie: Yeah, I learned it in daycare. But don't worry, I know I'm not supposed to say it.
Me: Oh... well... How about you get to say it to me once, just to get it out of your system. I promise I won't get mad. 
Natalie: I don't want to.
Me: Well, let's just hear it this once, so we can talk about what it means...
Natalie: No...
Me: It's okay...
Natalie: Okay, I'll say it just this once... the S-word is: Stupid!

Well, not really what I expected, but I'm very proud that she knows that is not a nice word to say!