Opposed to or contrary to nature; artificial, synthetic, or fundamentally against natural processes or principles.
From anti- (against) + natural (of or from nature). This term has been used since at least the 17th century to describe things that violate natural laws or processes.
Interestingly, humans often call something 'antinatural' when we're just unfamiliar with it—early critics said airplanes and electricity were 'antinatural,' but humans have always been part of nature, so our inventions kind of are too.
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