master key

American

noun

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

master key British

noun

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

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of master key

First recorded in 1570–80

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

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

From Science Daily • Jan. 9, 2026

At 15:19, she tried the door to the toilet, using a master key to unlock it.

From BBC • Oct. 21, 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

Why it's important: Your SSN is a master key to your financial life.

From Salon • Aug. 27, 2024

Matthias slipped the master key from around Brum’s neck and dragged him into an empty cell, propping him up against the wall in a seated position.

From "Six of Crows" by Leigh Bardugo

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023