Contranyms

The shorties have had some good ones lately. The shorter of the short people asked me if there was a name for pairs of words that spell each other backwards like "pots" and "stop." Anyone know if there is such a term? I came up with "contranym" where palindromes would become autocontranyms.

Five letter ones are easy enough to come up with -- parts and strap, for example, or snaps and spans. Can we find ones that are even longer?