It’ll unlock several doors (6,3)

I believe the answer is:

master key

(Other definitions for master key that I've seen before include "All-round opener" , "Passe-partout" , "one readily admits!" , "Locker" , "most useful of the bunch?" .)

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.