main

(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”

Most important element.

“the main doors were of solid glass”

Of force; of the greatest possible intensity.

“by main strength”

Any very large body of (salt) water.

A principal pipe in a system that distributes water or gas or electricity or that collects sewage.