In a manner relating to, characteristic of, or in accordance with atheism; with disbelief in or denial of gods.
From 'atheistic' + the adverbial suffix '-ally.' The suffix converts the adjective into an adverb describing how an action is performed or a state exists.
Philosophers debated whether someone acting 'atheistically' (without believing in divine reward or punishment) could still be moral—this argument shaped modern ethics and is still discussed today!
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