Noun

1. Approval, agreement, or instruction to begin or proceed.

   You can start as soon as you get the go-ahead from the president.

Adjective

1. A score which gives the scoring team or player the lead in the game.

   The pitcher gave up the go-ahead run in the top of the ninth inning.

2. Progressive; exerting leadership.
   • 1906, Arthur Lincoln Haydon, The Book of the V. C., page 150

     This turbulent ruler was a very go-ahead monarch indeed. He organised a splendid army, well-drilled and well-equipped with modern arms