Bidirectional Words

So, this morning driving into school, the older of the short people asks me if there is a name for the class of words that spell a different word backwards. Palindromes are the special case where it is the same word in either direction, but what of the more general case where you get two different words? Is there a name for that?

She came up with a number of three and four letter examples -- saw/was, tool/loot, stop/pots. I mentioned the classic eight letter instance desserts/stressed. Others that you can think of? What is the longest?