The Collaborative International Dictionary of English v.0.48:

Main \Main\, n. [AS. m[ae]gen strength, power, force; akin to
   OHG. magan, Icel. megin, and to E. may, v. [root]103. See
   May, v.]
   1. Strength; force; might; violent effort. [Obs., except in
      certain phrases.]
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            There were in this battle of most might and main.
                                                  --R. of Gl.
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            He 'gan advance,
            With huge force, and with importable main.
                                                  --Spenser.
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   2. The chief or principal part; the main or most important
      thing. [Obs., except in special uses.]
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            Resolved to rest upon the title of Lancaster as the
            main, and to use the other two . . . but as
            supporters.                           --Bacon.
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   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.
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   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.
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            With might and main they chased the murderous fox.
                                                  --Dryden.
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The Collaborative International Dictionary of English v.0.48:

Might \Might\, n. [AS. meaht, miht, from the root of magan to be
   able, E. may; akin to D. magt, OS. maht, G. macht, Icel.
   m[=a]ttr, Goth. mahts. [root]103. See May, v.]
   Force or power of any kind, whether of body or mind; energy
   or intensity of purpose, feeling, or action; means or
   resources to effect an object; strength; force; power;
   ability; capacity.
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         What so strong,
         But wanting rest, will also want of might? --Spenser.
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         Thou shalt love the Lord thy God with all thine heart,
         and with all thy soul, and with all thy might. --Deut.
                                                  vi. 5.
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   With might and main. See under 2d Main.
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