grammar vs main

grammar and main both are nouns.

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

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

grammar (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