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

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

Fitzwater has also become a member of Crohn's and Colitis UK, who have given him a special card and a master key which allows him to access more than 9,000 locked public toilets.

From BBC • Feb. 15, 2024

“They must have some way to let people in. Do they have a master key in the office?”

From "Tangerine" by Edward Bloor

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