The quality, state, or condition of being atheistic; the extent to which something exhibits characteristics of atheism.
From 'atheistic' + '-ness,' forming an abstract noun. This is the more common modern variant of the older 'atheisticalness,' following standard English word-formation patterns.
The shift from 'atheisticalness' to 'atheisticness' mirrors how English gradually simplified its word formations—showing that even how we describe non-belief has evolved over centuries!
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