Synonyms

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

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

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