Heh, I remember from some book of useless knowledge, that the word was originally coined by some athiest that was sick of being called an athiest, so one day he came back by saying, "I'm agnostic"
But now it means you believe in something, but as to what it is? who knows. I think its acceptable. Simply because what you are looking for past that is what exactly do they think? Well if you believe in God, there are so many interpretations nowadays that you need more description from them. Even then you could get more description from an atheist, as "i don't believe in him" isn't always the reason either.