Ali Baba's magic words (4,6)
I believe the answer is:
open sesame
'ali baba's magic words' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for open sesame that I've seen before include "Magical words" , "Magic password" , "Spell from Ali Baba and the Forty Thieves" , "a very successful means of achieving a result" , "spelling words?" .)