1) GOOD Music single 2) Green symbol 3) Slang for official approval 
Approval for landing. A carryover expression from days when aircraft for the most part had no radios, and communication from a control tower was by means of a light-gun that beamed various green, red, and yellow signals to pilots in the air and on the ground. A popular phrase, "3 green lights," refers to the instrument panel lights verifying that a...
A light behind the goal cage, next to the red light, that goes on when time has expired in a period.
Green light is slang for official approval.
[n] - the signal to proceed
A phrase utilized by a coach to give a batsman a fit or a “green light” in the right position into the strike area of the batsman. It is the permission of the manager to batsman or runner to perform forcefully.
go-ahead noun a signal to proceed