main1
  
  adj.
 chief in size or importance.
n.
   - a principal pipe carrying water or gas or a cable carrying electricity. 
▸
(the mains)
 Brit. the source of public water, gas, or electricity supply through pipes or cables.
 - 
(the main)
 archaic or literary the open ocean.
 - Nautical  short for mainsail or mainmast.
 
 
  Phrase
  
    - by main force
 through sheer strength.  - in the main
 on the whole. 
   
  Etymology
  ME: from OE mægen ‘physical force’, reinforced by ON meginn, megn ‘strong, powerful’, both from a Gmc base meaning ‘have power’.
 
  
    
main2
  
  n.
  - (in the game of hazard) a number (5, 6, 7, 8, or 9) called by a player before dice are thrown.
 - historical a match between fighting cocks.
 
 
  Etymology
  C16: prob. from the phr. main chance.