chef-d'oeuvre vs piece of work

chef-d'oeuvre and piece of work both are nouns.

Word	Noun	Adjective	Verb	Adverb
chef-d'oeuvre	Yes	No	No	No
piece of work	Yes	No	No	No

As nouns, piece of work is a hypernym of chef-d'oeuvre; that is, piece of work is a word with a broader meaning than chef-d'oeuvre:

chef-d'oeuvre: the most outstanding work of a creative artist or craftsman
piece of work: a product produced or accomplished through the effort or activity or agency of a person or thing

Other hypernyms of chef-d'oeuvre include work.

chef-d'oeuvre (noun)	piece of work (noun)
the most outstanding work of a creative artist or craftsman	a product produced or accomplished through the effort or activity or agency of a person or thing