master key

a key that will open a number of different locks, the proper keys of which are not interchangeable.

Origin of master key

First recorded in 1570–80

But the clerks rushed to the office to see what had become of the master-key, and found it gone.

More Tales by Polish Authors |Various
Now, one other thing: the housekeeper must have a master-key that opens all the bedrooms in the place.

Cleek, the Master Detective |Thomas W. Hanshew
Then it was no particular secret, the master-key and its hiding place?

In Jeopardy |Van Tassel Sutphen
The drawing itself was based on a system of master-key numbers in two groups, written on slips of paper.

The Story of the Great War, Volume VI (of VIII) |Various

Once you have the master-key, you may unlock many doors of mystery which have heretofore been closed to you.

Clairvoyance and Occult Powers |Swami Panchadasi

master key

a key that opens all the locks of a set, the individual keys of which are not interchangeable Also called: pass key