Officially, a word becomes a word when it's added to an English language dictionary. Personally, I think a word is anything that is understood when communicated to another person.

I've never heard misconsidered before, but I instantly know what you're referring to by its structure and similarity to words I do know.

Is funnier not in any dictionary? I'm surprised... again though, I know exactly what it is so I'd consider it a word. Words are just a means to communicate... as long as the message is recieved.