main

nouns

any very large body of (salt) water
a principal pipe in a system that distributes water or gas or electricity or that collects sewage
is a part of
the stock of basic facilities and capital equipment needed for the functioning of a country or area
"the industrial base of Japan"
is a type of (narrower)
a long tube made of metal or plastic that is used to carry water or oil or gas etc.

adjectives

most important element
"the chief aim of living"; "the main doors were of solid glass"; "the principal rivers of America"; "the principal example"; "policemen were primary targets"; "the master bedroom"; "a master switch"
(of a clause) capable of standing syntactically alone as a complete sentence
"the main (or independent) clause in a complex sentence has at least a subject and a verb"
of force; of the greatest possible intensity
"by main strength"
is similar to
possessing or displaying a distinctive feature to a heightened degree
"intense heat"; "intense anxiety"; "intense desire"; "intense emotion"; "the skunk's intense acrid odor"; "intense pain"; "enemy fire was intense"