Source : Webster's Revised Unabridged Dictionary (1913)

Main \Main\, a. [From {Main} strength, possibly influenced by
   OF. maine, magne, great, L. magnus. Cf. {Magnate}.]
   1. Very or extremely strong. [Obs.]

            That current with main fury ran.      --Daniel.

   2. Vast; huge. [Obs.] ``The main abyss.'' --Milton.

   3. Unqualified; absolute; entire; sheer. [Obs.] ``It's a man
      untruth.'' --Sir W. Scott.

   4. Principal; chief; first in size, rank, importance, etc.

            Our main interest is to be happy as we can.
                                                  --Tillotson.

   5. Important; necessary. [Obs.]

            That which thou aright Believest so main to our
            success, I bring.                     --Milton.

   {By main force}, by mere force or sheer force; by violent
      effort; as, to subdue insurrection by main force.

            That Maine which by main force Warwick did win.
                                                  --Shak.

   {By main strength}, by sheer strength; as, to lift a heavy
      weight by main strength.

   {Main beam} (Steam Engine), working beam.

   {Main boom} (Naut.), the boom which extends the foot of the
      mainsail in a fore and aft vessel.

   {Main brace}.
      (a) (Mech.) The brace which resists the chief strain. Cf.
          {Counter brace}.
      (b) (Naut.) The brace attached to the main yard.

   {Main center} (Steam Engine), a shaft upon which a working
      beam or side lever swings.

   {Main chance}. See under {Chance}.

   {Main couple} (Arch.), the principal truss in a roof.

   {Main deck} (Naut.), the deck next below the spar deck; the
      principal deck.

   {Main keel} (Naut.), the principal or true keel of a vessel,
      as distinguished from the false keel.

   Syn: Principal; chief; leading; cardinal; capital.