Source : Webster's Revised Unabridged Dictionary (1913)

Main \Main\, n. [F. main hand, L. manus. See {Manual}.]
   1. A hand or match at dice. --Prior. Thackeray.

   2. A stake played for at dice. [Obs.] --Shak.

   3. The largest throw in a match at dice; a throw at dice
      within given limits, as in the game of hazard.

   4. A match at cockfighting. ``My lord would ride twenty miles
      . . . to see a main fought.'' --Thackeray.

   5. A main-hamper. [Obs.] --Ainsworth.

Main \Main\, n. [AS. m[ae]gen strength, power, force; akin to
   OHG. magan, Icel. megin, and to E. may, v. ?. See {May}, v.]
   1. Strength; force; might; violent effort. [Obs., except in
      certain phrases.]

            There were in this battle of most might and main.
                                                  --R. of Gl.

            He 'gan advance, With huge force, and with
            importable main.                      --Spenser.

   2. The chief or principal part; the main or most important
      thing. [Obs., except in special uses.]

            Resolved to rest upon the title of Lancaster as the
            main, and to use the other two . . . but as
            supporters.                           --Bacon.

   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.

   {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.

            With might and main they chased the murderous fox.
                                                  --Dryden.

Main \Main\, adv. [See {Main}, a.]
   Very; extremely; as, main heavy. ``I'm main dry.'' --Foote.
   [Obs. or Low]

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.

Source : WordNet®

main
     n 1: any very large body of (salt) water [syn: {briny}]
     2: a principal pipe in a system that distributes water or gas
        or electricity or that collects sewage

main
     adj 1: 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" [syn: {chief(a)}, {main(a)}, {primary(a)},
             {principal(a)}]
     2: 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" [syn: {independent},
         {main(a)}] [ant: {dependent}]
     3: of force; of the greatest possible intensity; "by main
        strength" [syn: {main(a)}]