sewer main vs main

sewer main and main both are nouns.

Word	Noun	Adjective	Verb	Adverb
sewer main	Yes	No	No	No
main	Yes	Yes	No	No

As nouns, main is a hypernym of sewer main; that is, main is a word with a broader meaning than sewer main:

sewer main: a main in a sewage system
main: a principal pipe in a system that distributes water or gas or electricity or that collects sewage

sewer main (noun)	main (noun)
a main in a sewage system	a principal pipe in a system that distributes water or gas or electricity or that collects sewage
	any very large body of (salt) water

sewer main (adjective)	main (adjective)
	(of a clause) capable of standing syntactically alone as a complete sentence
	most important element
	of force; of the greatest possible intensity