Longman Dictionary of Contemporary English - main

~1 adj only before noun 1 bigger or more important than all other things, ideas, influences etc of the same kind  (I noted down the main points of her speech. | The main bedroom is at the back of the house. | Lack of confidence was the main reason behind the team's defeat. | Our main concern is that the children are safe. | The main female character in the movie.) 2 the main thing spoken used to say what is the most important thing in a situation  (As long as you're not hurt, that's the main thing. | The main thing is not to panic.)  (- see also with an eye to the main chance eye1 (36), the main drag drag2 (7)) ~2 n 1 a large pipe or wire carrying the public supply of water, electricity or gas  (a burst water main in the street) 2 the mains BrE a) the place on a wall you can connect something to a supply of electricity  (You can run it off batteries or plug it into the mains. | at the mains)  (Make sure that the television is turned off at the mains.) b) mains gas/electricity/water The public supply of gas etc through large pipes or wires  (The heater will run off mains gas or bottled gas.) 3 in the main mostly  (Her fellow students were in the main from wealthy backgrounds.)  (- see also with might and main might2 (1))