phone system vs MEDLINE

phone system and MEDLINE both are nouns.

Word	Noun	Adjective	Verb	Adverb
phone system	Yes	No	No	No
MEDLINE	Yes	No	No	No

As nouns, MEDLINE is a hyponym of phone system; that is, MEDLINE is a word with a more specific, narrower meaning than phone system:

phone system: a communication system that transmits sound between distant points
MEDLINE: the computer-based telephone system of the United States National Library of Medicine that provides rapid linkage to MEDLARS

phone system (noun)	MEDLINE (noun)
a communication system that transmits sound between distant points	the computer-based telephone system of the United States National Library of Medicine that provides rapid linkage to MEDLARS