One Russian root word for navel is пуп. That's enough to make any American laugh. And most of us will be so amused that we aren't going to bother to investigate the word further. But here at Russian Word of the Day we pride ourselves on taking interest in all sorts of things that other people simply ignore, and today the belly button is it. It is an end-stressed noun, so it declines like this:

I know, I know: the dative singular made you laugh again.

Anyhoo, пуп is etymologically the source word for navel, one that you will find once in a blue moon in a formal, scientific, or medical context. Thus Russian Wikipedia gives us this info:

But when talking about a person's belly button, the Russians almost never say пуп. Instead they use the end-stressed diminutive пупок.

Sometimes you see belly dancers in movies and you can see their navels, but my mother, who used to take belly dancing classes, tells me that that is a no-no:

Every five or ten years I get into a conversation about the lint that can show up in one's belly button. It seems to be a gender based issue: men have it happen more often than women. Тhe subject was even brought up recently on the web:

One of the amazing things about Russian is that you can make a diminutive of a diminutive, so the dimiminutive of the diminutive пупок is — are you ready for the? — пупочек. This one turns out to be stem stressed:

The word is mostly used to refer to a baby's belly button. There is a bit of a gender difference in the use of this word. Adult men will rarely use it. Mothers and grandmothers will use it more often. (I actually had one Russian man tell me no one used it, but that's simply not true.) For instance, on babyblog.ru I found this little gem:

And as long as we are talking about belly buttons, we should mention the English word omphaloskepsis, which is meditation using the belly button as a focus. That's got nothing to do with Russian. I just really like the word.