4-year-old (In sweet lispy 4-year-old voice): "Mommy, what does 'fat' mean?"
Me (In an absent-minded, lazy voice): "It means 'big.'"
4-year-old: "Mommy, you are very, very fat!"
Me (In a paying-attention-now voice): "Honey, many people don't like it when you call them fat. It means they are...uh...bigger than they'd like to be."
4-year-old: "Mommy you are bigger than me!" (OK. I can agree with that.)
I suppose I should have told her that "fat" means, "having too much adipose tissue." (see below). That would have cleared things right up.
P.S. I really don't have a problem with the word "fat" myself (not that I want people yelling it at me in the street), but I don't want 4-year-old to start telling anyone who is larger than she is that they are "fat."