[1] : The Collaborative International Dictionary of English v.0.48

main \main\, n. as. maegen strength, power, force; akin to
   ohg. magan, icel. megin, and to e. may, v. root103. see
   may, v.
   1. strength; force; might; violent effort. obs., except in
      certain phrases.
      1913 webster

            there were in this battle of most might and main.
                                                  --r. of gl.
      1913 webster

            he 'gan advance,
            with huge force, and with importable main.
                                                  --spenser.
      1913 webster

   2. the chief or principal part; the main or most important
      thing. obs., except in special uses.
      1913 webster

            resolved to rest upon the title of lancaster as the
            main, and to use the other two . . . but as
            supporters.                           --bacon.
      1913 webster

   3. specifically:
      a the great sea, as distinguished from an arm, bay,
          etc.; the high sea; the ocean. "struggling in the
          main." --dryden.
      b the continent, as distinguished from an island; the
          mainland. "invaded the main of spain." --bacon.
      c principal duct or pipe, as distinguished from lesser
          ones; esp. engin., a principal pipe leading to or
          from a reservoir; as, a fire main.
          1913 webster

   forcing main, the delivery pipe of a pump.

   for the main, or in the main, for the most part; in the
      greatest part.

   with might and main, or with all one's might and main,
      with all one's strength; with violent effort.
      1913 webster

            with might and main they chased the murderous fox.
                                                  --dryden.
      1913 webster
see also:
may forcing main for the main in the main with might and main with all one's might and main 

[2] : WordNet (r) 2.0

in the main
     adv 1: for the most part; "he is mainly interested in butterflies"
            syn: chiefly, principally, primarily, mainly
     2: without distinction of one from others; "he is interested in
        snakes in general" syn: generally, in general ant:
        specifically
see also:
chiefly principally primarily mainly generally in general 
specifically 

Main >> M Words
Main, definition of term: Main
main_pag1.html

Main Road >> M Words
Main Road, definition of term: Main Road
main+road_pag1.html

Main Street >> M Words
Main Street, definition of term: Main Street
main+street_pag1.html

Main Memory >> M Words
Main Memory, definition of term: Main Memory
main+memory_pag1.html

Main Line >> M Words
Main Line, definition of term: Main Line
main+line_pag1.html

Main Brace >> M Words
Main Brace, definition of term: Main Brace
main+brace_pag1.html

Main Distributi >> M Words
Main Distributi, definition of term: Main Distributi
main+distributi_pag1.html