main vs grammar

main and grammar both are nouns.

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

main (noun)	grammar (noun)
a principal pipe in a system that distributes water or gas or electricity or that collects sewage	the branch of linguistics that deals with syntax and morphology (and sometimes also deals with semantics)
any very large body of (salt) water

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