Relating to or measured along a diameter; representing exact or absolute opposition or contrast.
From Latin 'diametricus', derived from 'diameter'. Similar to 'diametral' but perhaps slightly more common in modern usage, especially in the phrase 'diametric opposite'.
The phrase 'diametric opposite' is everywhere—but it's technically redundant since 'opposite' already means the same thing. However, it adds dramatic emphasis, which is why writers and speakers can't resist piling on that geometric wordplay.
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