To contaminate or corrupt jointly; to make something unclean together with others.
From co- (together) + inquinate (from Latin inquinare: in- (in) + quina- (to soil)). A rare learned term combining Latin elements, likely formed by analogy with similar co- verbs.
This is an almost untraceable word in English literature—it's technically constructible from Latin roots but barely used. It illustrates how you can build words from ancient roots even if nobody ever bothers to use them.
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