Atheism (A'thE-iz"um),-n, is defined as:
1. the doctrine or belief that there is no God.
2. disbelief in the existence of a supreme being or beings.
The term atheism comes from the Greek word atheos, meaning godless. Atheos is derived form a, meaning "without," and theos, meaning "deity".
non-believer synonyms: agnostic, atheist, bright, disbeliever, doubter, faithless, freethinker, godless, heretic, ill religious, infidel, materialist, nihilist, non-believer, non-religious, objectivist, rationalist, secularist, skeptic, unbeliever
Thanks to Atheist Empire for definition.