storm drain vs drain system

storm drain and drain system both are nouns.

Word	Noun	Adjective	Verb	Adverb
storm drain	Yes	No	No	No
drain system	Yes	No	No	No

As nouns, storm drain and drain system are synonyms defined as:

storm drain and drain system: a system of watercourses or drains for carrying off excess water

Other synonyms of storm drain include drainage well, storm sewer, stormwater drain.

storm drain (noun)	drain system (noun)
a system of watercourses or drains for carrying off excess water	a system of watercourses or drains for carrying off excess water