sui generis:
Sui generis (/ˌsuːiˈdʒɛnərɪs/ SOO-ee JEN-ər-iss,[1] Latin: [ˈsʊ.iː ˈɡɛnɛrɪs]) is a Latin phrase that means “of its/his/her/their own kind, in a class by itself”, therefore “unique”. [Wikipedia]
Noted in “Don’t blame George W. Bush for the GOP’s authoritarianism. It’s Trump’s fault,” Max Boot, WaPo:
Was President Donald Trump sui generis? Or was he merely the product of forces that had been gathering in the Republican Party for years?