Co-operation between the two great fighting services is the master-key opening every impeditive doorway on the path to victory.
She had provided herself with a master-key which opened all the doors.
His enemies asserted, by the way, that a strong trustfulness in sounds and forms was the master-key to Mr Pecksniff's character.
Love is the master-key that opens every ward of the heart of man.
If the machinery flagged, she at once applied the master-key of her energy, and the wheels went on again.
The mystery of Sex is, surely, master-key to all the other mysteries of the Cosmos.
In fact Rabelais gives us (as the greatest writers so often do) what is in more senses than one a master-key to the contrast.
Then it didn't occur to you that you might use the master-key?
For a second only he hesitated, then swiftly fitted the master-key and opened the door.
With a master-key the chambers of their souls can one after another be unlocked.