library vs bibliotheca

library and bibliotheca both are nouns.

Word	Noun	Adjective	Verb	Adverb
library	Yes	No	No	No
bibliotheca	Yes	No	No	No

As nouns, bibliotheca is a hyponym of library; that is, bibliotheca is a word with a more specific, narrower meaning than library:

library: a collection of literary documents or records kept for reference or borrowing
bibliotheca: a collection of books

Other hyponyms of library include public library, rental collection.

library (noun)	bibliotheca (noun)
a depository built to contain books and other materials for reading and study	a collection of books
a room where books are kept
a building that houses a collection of books and other materials
a collection of literary documents or records kept for reference or borrowing
(computing) a collection of standard programs and subroutines that are stored and available for immediate use