In the phrase 'sui generis,' meaning unique or in a category of its own; one-of-a-kind.
From Latin 'sui generis'—'sui' (of its own) + 'generis' (of a kind or genus). Used in English legal, scientific, and formal contexts since the 1700s.
Scientists use 'sui generis' to describe organisms that don't fit neatly into categories—like the platypus, which is so weird it seemed like a hoax when first discovered!
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