Permission, esp a superior's approval to proceed; the GO-AHEAD: When she got the green light, she invited the couple to see her in Washington/ have also been given the green light to advertise special plates(1937+)
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with green light, the
green light, the
Permission to go ahead, as in The chief gave us the green light for starting this project. This term originated in the late 1800s for the signal used by railroads to indicate that a train could proceed. It was transferred to more general use in the first half of the 1900s.