main main /ˈmeɪn/

adjective

1. () Most important element  ( master , primary , chief , main , principal )
   most important element
    The chief aim of living
   the chief aim of living
    The main doors were of solid glass
   the main doors were of solid glass
    The principal rivers of America
   the principal rivers of America
    The principal example
   the principal example
    Policemen were primary targets
   policemen were primary targets
    The master bedroom
   the master bedroom
    A master switch
   a master switch
   
2. (of a clause) capable of standing syntactically alone as a complete sentence  ( independent , 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
   the main (or independent) clause in a complex sentence has at least a subject and a verb
   
3. Of force; of the greatest possible intensity  ( main )
   of force; of the greatest possible intensity
    By main strength
   by main strength
   

noun

1. A principal pipe in a system that distributes water, gas, electricity or that collects sewage  ( main )
   a principal pipe in a system that distributes water, gas, electricity or that collects sewage
   
2. Any very large body of (salt) water  ( briny [British] , main )
   any very large body of (salt) water