main

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Most important; principal. synonym: chief.
• adjective Exerted to the utmost; sheer.
• adjective Nautical Connected to or located near the mainmast.
• adjective Obsolete Of or relating to a continuous area or stretch, as of land or water.
• noun The chief or largest part.
• noun The principal pipe or conduit in a system for conveying water, gas, oil, or other utility.
• noun Physical strength.
• noun A mainland.
• noun The open ocean.
• noun A mainsail.
• noun A mainmast.

from The Century Dictionary.

• Mightily; exceedingly; extremely.
• To furl: said of sails.
• Great in size or degree; vast; hence, strong; powerful; important.
• Principal; prime; chief; leading; of chief or principal importance: as, his main effort was to please.
• Principal or chief in size or extent; largest; consisting of the largest part; most important by reason of size or strength: as, the main timbers of a building; the main branch of a river; the main body of an army.
• Full; undivided; sheer: now used chiefly in the phrases main strength, main force.
• Nautical, belonging to or connected with the principal mast in a vessel.
• “Big”; angry.
• noun A hand.
• noun . A hand at dice; a throw of the dice at hazard.
• noun A match at cock-fighting.
• noun A banker's shovel for coin.
• An obsolete variant of maim.
• noun Strength; force; violent effort: now used chiefly in the phrase with might and main.
• noun That which is chief or principal; the chief or main portion; the gross; the bulk; the greater part.
• noun The principal point; that which is of most importance; the chief or principal object, aim, or effort.
• noun A broad expanse, as of space or light; unbroken extent; full sweep or stretch.
• noun Now, specifically
• noun The expanse of ocean; the open ocean; the high sea.
• noun A continental stretch of land; a continent; the maiuland, as distinguished from islands.
• noun A principal duct, channel, pipe, or electrical conductor, as a water- or gas-pipe running along a street in a town, or the largest conductor in a system of electric lights.
• noun The thick part of meat.

from the GNU version of the Collaborative International Dictionary of English.

• noun A hand or match at dice.
• noun obsolete A stake played for at dice.
• noun The largest throw in a match at dice; a throw at dice within given limits, as in the game of hazard.
• noun A match at cockfighting.
• noun obsolete A main-hamper.
• noun Obs., except in certain phrases. Strength; force; might; violent effort.
• noun Obs., except in special uses. The chief or principal part; the main or most important thing.
• noun The great sea, as distinguished from an arm, bay, etc. ; the high sea; the ocean.
• noun The continent, as distinguished from an island; the mainland.
• noun principal duct or pipe, as distinguished from lesser ones; esp. (Engin.), a principal pipe leading to or from a reservoir.
• noun the delivery pipe of a pump.
• noun for the most part; in the greatest part.
• noun with all one's strength; with violent effort.