In reply to:

Is there a -nym for words that are a different word when read backwards, like "dog" and "god," or "pot" and "top"? What's the longest that you know?

my latest, greatest favoritist word site (well, besides this one) offers the simple term "reversal", and says that D-E-S-S-E-R-T-S / S-T-R-E-S-S-E-D is the longest such phenomenon.