curate's egg

 
Pronunciation: /kjʊərətsˈɛɡ/

noun

British
  • a thing that is partly good and partly bad: this book is a bit of a curate’s egg

Origin:

early 20th century: from a cartoon in Punch (1895) depicting a meek curate who, given a stale egg at the bishop's table, assures his host that ‘parts of it are excellent’