I’m not sure I understand your question fully. Are you looking for two words with the same/similar meaning and etymology but with completely reversed letters? That’s not going to happen in alphabetic languages, because it’s simply not how languages work - completely reversing the actual sounds that come out of your mouth is a phonetic impossibility.

You will be able to find examples where two morphemes have swapped places, similar to your manners/etiquette example, but usually the meaning will change too. The first example that came to my mind is boathouse / houseboat - the former is a building used to store boats, the latter is a boat which is also a dwelling.