Bad Words

My family has been discussing curse words and what makes a word "BAD"
The reason being my youngest ,Ethan, got very mad playing a video game and said a not proper for a 6 year old word.
My oldest, Elijah spelled what he said so he would not get in trouble. Then I wondered how an 8 year old knew how to spell it!
So I sent Ethan to his room to interrogate him. Turns out he didn't even know what he had said or what it meant so he escaped the soap for now. The problem arises in parenting when your child asks a question you just don't know the answer too. He asked" Why are there bad words?"
My answer "well, um, Why don't you stay in your room and ask God"
Cop-out I know but I didn't know what to say that he would understand.
The amazing thing is what he came up with.
Later he came up to me and said " The devil made up bad words so that we would get in trouble."
I don't know if that is a good way for him to think, but at least he hasn't said "the word" since.