bookcase vs piece of furniture

bookcase and piece of furniture both are nouns.

Word	Noun	Adjective	Verb	Adverb
bookcase	Yes	No	No	No
piece of furniture	Yes	No	No	No

As nouns, piece of furniture is a hypernym of bookcase; that is, piece of furniture is a word with a broader meaning than bookcase:

bookcase: a piece of furniture with shelves for storing books
piece of furniture: furnishings that make a room or other area ready for occupancy

Other hypernyms of bookcase include article of furniture, furniture.

bookcase (noun)	piece of furniture (noun)
a piece of furniture with shelves for storing books	furnishings that make a room or other area ready for occupancy