May Russian [woina] ([война]) "war" derive from [boinia] ([бойня]) "slaughtering"?
Slovak [bojovat'] is interesting! Russian has [wojewat']. Also, Russian [wojenny] "military" and [bojets] "soldier" have equal meaning.Well, e.g. in Slovak we have boj (battle) and vojna (war). Also various derivates as bojovať (to fight, to battle, ...), vojak (soldier), etc ... So if I do understand your previous post (#2) well, then the words boj and vojna are etymologically unrelated. Is it so? ...
Perhaps no (at least I've not noticed). But there may be other reasons ("exceptions") as well, see e.g. the answer of rushalaim (#5): bojovať versus vojevať .Is there a single instance of interchange of b and v in Slavic ... ?