main vs territorial waters

main and territorial waters both are nouns.

Word	Noun	Adjective	Verb	Adverb
main	Yes	Yes	No	No
territorial waters	Yes	No	No	No

main (noun)	territorial waters (noun)
a principal pipe in a system that distributes water or gas or electricity or that collects sewage	the waters surrounding a nation and its territories over which that nation exercises sovereign jurisdiction
any very large body of (salt) water

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