security system vs computer science

security system and computer science both are nouns.

Word	Noun	Adjective	Verb	Adverb
security system	Yes	No	No	No
computer science	Yes	No	No	No

security system (noun)	computer science (noun)
an electrical device that sets off an alarm when someone tries to break in	the branch of engineering science that studies (with the aid of computers) computable processes and structures
(computing) a system that enforces boundaries between computer networks