drain system vs storm drain

drain system and storm drain both are nouns.

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

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

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

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

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