Augustus
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Atheism means "without theism." That's why the "a" is in front of the word "theism" - it means "without."
That's simply not true though. Factually, at least per the OED, the etymology is athe(os)-ism, not a-theism (the term atheism even predates the term theism).
If we are making an 'argument from etymology', athe-ism thus means 'the doctrine or belief of being without god(s)' as it was an -ism suffix being applied to atheos, not an a- prefix being applied to (the then non-existent term) theism .
Ultimately though, an argument from etymology doesn't really carry much weight anyway. It changes nothing as it is still a subject preference to use the more traditional 'a belief no gods exist' definition or the more recent addition 'a lack of belief in gods' as it would be with any other term with multiple usages that evolved over time.