We need a word for this!

A palindrome has the same meaning whether it is spelled forward or backward. "Tenet" is an example.

What do we call something that has exactly the opposite meaning when it is spelled backward? 

Take a look at this contest winner (second place) by a 20-year-old woman. It's worth your time (a bit over a minute). 

If you can think of a word to describe it, please comment!

Thanks to Steve Cook of Frederick, MD for sending this link.