"Permission granted" (3)
'permission granted' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for yes that I've seen before include "Confirmation" , "Absolutely" , "Yea" , "I agree" , "That's 27 [RIGHT]" .)
(Other definitions for go ahead that I've seen before include "Up-and-coming -- authorisation" , "Ambitious" , "Enterprising (2 5); continue" , "[ENERGETIC]" , "Lead" .)