nonpareil vs unknown quantity

nonpareil

noun
  • A person or thing that has no equal; a paragon. 

  • A small, flat chocolate drop covered with such pellets of sugar, similar to a comfit. 

  • The blue underwing or Clifden nonpareil (Catocala fraxini), a species of moth distributed across the Palearctic; also (obsolete) any of a number of moths of other species. 

  • A caper (“pickled edible flower bud”) of the smallest size. 

  • The painted bunting (Passerina ciris), a brightly-coloured finch native to North America. 

  • The size of type between ruby and emerald (or, in the United States, between agate and minion), standardized as 6-point; (countable) a slug of this size. 

adj
  • Unequalled, unrivalled; unique. 

unknown quantity

noun
  • A person or thing whose nature or value is a mystery. 

  • Used other than figuratively or idiomatically: see unknown, quantity. 

How often have the words nonpareil and unknown quantity occurred in a corpus of books? (source: Google Ngram Viewer )