Funky, an "agnostic" is someone who doesn't know whether there is a God or not. The word comes from the Greek for "not knowing". Of course, technically *no-one* really *knows* whether there is a God or not, so the word normally refers to those who are not sure, that is, they believe there may be a God or there may not. Most people who believe in God (these days) think that God's existence cannot be proved. In fact this is generally accepted today as a given, even though this view is a relatively recent development and is condemned by the First Vatican Council, so a good Roman Catholic should tell you that not only does God exist but this fact can be proved.
Similarly, I fear the dictionary where you found the definition of "religion" is quite mistaken. It was evidently written by somone who only knows about modern Western religion. It would not include Buddhism; neither would it include the monotheism of Aristotled (who believed that the world was eternal and therefore not created). Scholars of religion spend much time today arguing about how religion should best be defined, but they all agree that it cannot be summed up in such a simplistic way.