What is the meaning of main?

noun

• Any very large body of (salt) water.
  • synonyms: briny
• A principal pipe in a system that distributes water or gas or electricity or that collects sewage.

adjective

• Most important element.
  • usage: "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"
  • synonyms: chief, primary, principal, master
• Of a clause. ( capable of standing syntactically alone as a complete sentence)
  • usage: "the main (or independent) clause in a complex sentence has at least a subject and a verb"
  • synonyms: independent
• Of force; of the greatest possible intensity.
  • usage: "by main strength"