Quietly retreat, then go ahead (7)
I believe the answer is:
precede
'go ahead' is the definition.
(thesaurus)
'quietly retreat' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'retreat' becomes 'recede' (receding is a kind of retreating).
'p'+'recede'='PRECEDE'
'then' acts as a link.
(Other definitions for precede that I've seen before include "Forerun" , "Pave the way" , "Go ahead of" , "be in the van" , "Come or go before" .)