The quality or state of being opposed to Christianity; the condition or fact of being antichristian.
From antichristian + -ity (state or condition of). This term is a parallel formation using the standard suffix -ity to create an abstract noun from the adjective antichristian.
Notice how English creates three different forms from the same root (antichristian, antichristianism, antichristianity)—this is called 'productive affixation' and shows language's incredible efficiency in generating related concepts.
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