chef d'œuvre vs piece of art

chef d'œuvre

noun
  • A work of outstanding creativity, skill or workmanship. 

  • A work created in order to qualify as a master craftsman and member of a guild. 

  • A piece of work that has been given much critical praise, especially one considered the greatest work of a person's career. 

piece of art

noun
  • Synonym of work of art 

How often have the words chef d'œuvre and piece of art occurred in a corpus of books? (source: Google Ngram Viewer )