on-line database vs database

on-line database and database both are nouns.

Word	Noun	Adjective	Verb	Adverb
on-line database	Yes	No	No	No
database	Yes	No	No	No

As nouns, database is a hypernym of on-line database; that is, database is a word with a broader meaning than on-line database:

on-line database: (computer science) a database that can be accessed by computers
database: an organized body of related information

on-line database (noun)	database (noun)
(computer science) a database that can be accessed by computers	an organized body of related information