What is the difference between a Gnostic and a Theist?
A Theist believes in (a) god/s, while an atheist believes that there isn't. An Agnostic professes that they have not/cannot have definite knowledge, while a Gnostic claims to know (as opposed of just believe) whether there is/isn't (a) god/s.
Gnostic also often refers to a specific flavor of Christianity, so don't mix these two definitions up.
I'd just like to point out that in its basic form, Atheism is agnostic and Atheists do not
believe anything about God(s). So statements about believing that there isn't' a god, or believing that there is nothing out there beyond our ability to scrutinize scientifically, those are faith-based statements and not true of basic Atheism.
Once you say 'I know there is no God', you become Anti-Theist, which is a gnostic position, and as scientifically unsound as saying 'I know there is a God'. (Anti-Theism may count as a form of Atheism, since Anti-Theists also do not have any Gods.)
Addendum: That is not to say that Atheists cannot also have faith-based beliefs, be gnostic, anti-theist, spiritual, or any other thing on the scale. Just that the very simplest, strictly literal form of it is a lack of belief in God, rather than a denial of existence of God.
