A palindrome is of course a word (e.g. tattarrattat, a knock at the door) or phrase (e.g. Norma is as selfless as I am Ron, my favourite) that reads the same forwards and backwards,.
But have you heard of the anadrome? An anadrome is a word the taken backwards gives a different, but perfectly good, word. The longest example in English is, as far as anyone knows, the 8-letter stressed and desserts.
I wrote a short program that searched a public-domain word list and found several 7-letter anadromes:
dessert
reviver
reifier
stinker
stellas
deifier
deified
deliver
reviled
rewarder
halalah
reified
sallets
reknits
stressed
sememes
redrawer
tressed
I rather like stinker and reknits.
If we consider shorter words there are many more anadromes: I found 397 of 2 or more letters in a list of 113809 words.
There are also some that have been made up: the unit of electrical resistance is the ohm and as far back as 1888 someone coined mho as a unit for the reciprocal of resistance, conductance. It's probably not official but I think it's quite common, I was certainly familiar with it. Another nice example I found on Wikipedia is tink, which means unknit (geddit?). This goes rather nicely with stinker and reknits, I feel.