'For the main' definitions:

Definition of 'For the main'

From: GCIDE

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. [1913 Webster]
He 'gan advance, With huge force, and with importable main. --Spenser. [1913 Webster]
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. [1913 Webster]
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]