storm sewer vs stormwater drain

storm sewer and stormwater drain both are nouns.

Word	Noun	Adjective	Verb	Adverb
storm sewer	Yes	No	No	No
stormwater drain	Yes	No	No	No

As nouns, storm sewer and stormwater drain are synonyms defined as:

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

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

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