Of a unique or special kind; in a class by itself (Latin phrase 'sui generis').
From Latin 'generis', the genitive form of 'genus' (kind, class, type). In English, this appears almost exclusively in the phrase 'sui generis' meaning 'of its own kind.'
When scientists describe a species as 'sui generis,' they mean it's so weird it might need its own genus—like when the platypus was discovered and seemed to break every rule of what a mammal should be.
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