What does "main" mean?

Additional senses

1. 2.The largest throw in a match at dice; a throw at dice within given limits, as in the game of hazard.
2. 3.A match at cockfighting. "My lord would ride twenty miles . . . to see a main fought." Thackeray.
3. 4.A main-hamper. [Obs.] Ainsworth.
4. 5.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.
5. 6.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.
6. 7.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.
7. 8.Very or extremely strong. [Obs.] That current with main fury ran. Daniel.
8. 9.Vast; huge. [Obs.] "The main abyss." Milton.
9. 10.Unqualified; absolute; entire; sheer. [Obs.] "It's a man untruth." Sir W. Scott.
10. 11.Principal; chief; first in size, rank, importance, etc. Our main interest is to be happy as we can. Tillotson.
11. 12.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.
12. 13.Very extremely; as, main heavy. "I'm main dry." Foote. [Obs. or Low]