master key

American  

noun

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

---

master key British  

noun

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

---

Etymology

Origin of master key

First recorded in 1570–80

Example Sentences

Professor Jonathan Heeney of Cambridge University likened the new technique to having the "master key" for an apartment block.

From Barron's • Jun. 25, 2026

Antibodies can sometimes act like a master key, helping trigger immune responses.

From Science Daily • Jan. 9, 2026

"As we have said many times before, we have never built a backdoor or master key to any of our products or services and we never will."

From BBC • Oct. 1, 2025

Mitchell also went into Blanchard’s chambers in 2023 by using a master key, the commission wrote.

From Los Angeles Times • Feb. 13, 2025

I had the master key because another one of my summer jobs was assistant apprentice super for my family’s complex.

From "The Epic Fail of Arturo Zamora" by Pablo Cartaya