1. [adj]  (grammar) of a clause; able to stand alone syntactically as a complete sentence; "the main (or independent) clause in a complex sentence has at least a subject and a verb"
2. [adj]  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"
3. [adj]  of force; of the greatest possible intensity; "by main strength"

MAIN(A) is a 7 letter word that starts with M.