The Collaborative International Dictionary of English v.0.48:

main \main\ (m[=a]n), n. [F. main hand, L. manus. See Manual.]
   1. A hand or match at dice. --Prior. --Thackeray.
      [1913 Webster]

   2. A stake played for at dice. [Obs.] --Shak.
      [1913 Webster]

   3. The largest throw in a match at dice; a throw at dice
      within given limits, as in the game of hazard.
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   4. A match at cockfighting. "My lord would ride twenty miles
      . . . to see a main fought." --Thackeray.
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   5. A main-hamper. [Obs.] --Ainsworth.
      [1913 Webster]

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.]
      [1913 Webster]

            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.]
      [1913 Webster]

            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.
          [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]

The Collaborative International Dictionary of English v.0.48:

Main \Main\ (m[=a]n), a. [From Main strength, possibly
   influenced by OF. maine, magne, great, L. magnus. Cf.
   Magnate.]
   1. Very or extremely strong. [Obs.]
      [1913 Webster]

            That current with main fury ran.      --Daniel.
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   2. Vast; huge. [Obs.] "The main abyss." --Milton.
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   3. Unqualified; absolute; entire; sheer. [Obs.] "It's a man
      untruth." --Sir W. Scott.
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   4. Principal; chief; first in size, rank, importance, etc.;
      as, the main reason to go; the main proponent.
      [1913 Webster +PJC]

            Our main interest is to be happy as we can.
                                                  --Tillotson.
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   5. Important; necessary. [Obs.]
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            That which thou aright
            Believest so main to our success, I bring. --Milton.
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   By main force, by mere force or sheer force; by violent
      effort; as, to subdue insurrection by main force.
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            That Maine which by main force Warwick did win.
                                                  --Shak.
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   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.
      [1913 Webster]

   Syn: Principal; chief; leading; cardinal; capital.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Main \Main\, adv. [See Main, a.]
   Very; extremely; as, main heavy. "I'm main dry." --Foote.
   [Obs. or Low]
   [1913 Webster]

WordNet (r) 3.0 (2006):

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"; "the master bedroom"; "a master switch"
           [syn: chief(a), main(a), primary(a),
           principal(a), master(a)]
    2: (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" [syn:
       independent, main(a)] [ant: dependent, subordinate]
    3: of force; of the greatest possible intensity; "by main
       strength"
    n 1: any very large body of (salt) water [syn: main, briny]
    2: a principal pipe in a system that distributes water or gas or
       electricity or that collects sewage

Moby Thesaurus II by Grady Ward, 1.0:

158 Moby Thesaurus words for "main":
   Africa, Antarctica, Asia, Australia, Eurasia, Eurasian landmass,
   Europe, North America, South America, absolute, all-absorbing,
   arch, awful, banner, basic, big, big drink, biggest, blue,
   blue water, brine, briny, brute, capital, cardinal, central,
   champion, channel, chief, cock, comprehensive, conduit,
   consequential, considerable, continent, controlling, crazy,
   critical, crowning, crucial, damned, deep, dominant, dreadful,
   drink, duct, effort, electric cable, energy, essential,
   exceedingly, exhaustive, extremely, fire main, first, focal,
   foremost, front, full, fundamental, gas main, grand, grave, great,
   greatest, head, headmost, heavy, hegemonic, high sea, high seas,
   highest, hydrosphere, in the main, intense, irresistible, landmass,
   largest, larruping, leading, line, magisterial, maiden, main sea,
   mainland, mainly, mains, major, master, maximum, mere, might,
   mighty, monstrous, necessary, ocean, ocean depths, ocean main,
   ocean sea, out-and-out, outstanding, overriding, overruling,
   paramount, particular, peninsula, pipe, pipeline, plain, plenary,
   power, power supply, powerful, predominant, predominating,
   preeminent, premier, preponderant, prevailing, primal, primary,
   prime, principal, pure, ranking, ruling, salt sea, salt water, sea,
   serious, sheer, sovereign, star, stellar, strength, strong,
   strongest, subcontinent, supereminent, supreme, thalassa,
   the bounding main, the brine, the briny, the briny deep, the deep,
   the deep sea, the seven seas, the vasty deep, tide, topflight,
   topmost, total, uppermost, utter, vigor, vital, water main



The Free On-line Dictionary of Computing (30 December 2018):

main

    The name of the subroutine called by the
   run-time system (RTS) when it executes a C program.  The
   RTS passes the program's command-line arguments to main as a
   count and an array of pointers to strings.  If the main
   subroutine returns then the program exits.

   Java has inheritted the name "main" from C but in Java it's
   more complicated of course.  The main routine must have a
   signature of exactly

    public static void main(String [])

   And it must be inside a public class with the same name as the
   source file where it is defined.

   (2008-11-12)