noun (1)
\ ˈkē How to pronounce key (audio) \

Definition of key

 (Entry 1 of 5)

1a : a usually metal instrument by which the bolt of a lock is turned
b : any of various devices having the form or function of such a key a key for winding a clock
2a : a means of gaining or preventing entrance, possession, or control
b : an instrumental or deciding factor the key to her success
3a : something that gives an explanation or identification or provides a solution the key to a riddle
b : a list of words or phrases giving an explanation of symbols or abbreviations a pronunciation key in a dictionary
c : an aid to interpretation or identification : clue a key to understanding their motivation
d : an arrangement of the salient characters of a group of plants or animals or of taxa designed to facilitate identification
e : a map legend
4a : a part to be depressed by a finger that serves as one unit of a keyboard also : a representation of such a key (such as a space delineated on a touch screen) Tiny keys on your iPhone's screen can be difficult to hit accurately. — Cherlynn Low
b : one of the levers of a keyboard musical instrument that actuates the mechanism and produces the tones
c : a lever that controls a vent in the side of a woodwind instrument or a valve in a brass instrument
5 : a system of tones and harmonies generated from a hierarchical scale of seven tones based on a tonic the key of G major
6a : characteristic style or tone
b : the tone or pitch of a voice
c : the predominant tone of a photograph with respect to its lightness or darkness
7 : a decoration or charm resembling a key
8 : a small switch for opening or closing an electric circuit a telegraph key
9 : the set of instructions governing the encipherment and decipherment of messages an encryption key
10 : a free-throw area in basketball : free throw lane a jump shot from the top of the key
11a(1) : cotter pin
(2) : cotter
b : a keystone in an arch
c : a small piece of wood or metal used as a wedge or for preventing motion between parts
12 : samara



Definition of key (Entry 2 of 5)

: extremely or crucially important key issues a key moment in the game a key member of the staff


keyed; keying; keys

Definition of key (Entry 3 of 5)

transitive verb

1 : to lock or secure with or as if with a key : fasten: such as
a : to secure (something, as a pulley on a shaft) by a key
b : to finish off (an arch) by inserting a keystone
2 : to regulate the musical pitch of key the strings
3 : to bring into harmony or conformity : make appropriate : attune remarks keyed to a situation
4 : to identify (a biological specimen) by a key (see key entry 1 sense 3d)
5 : to provide with identifying or explanatory cross-references instructions keyed to accompanying drawings— John Gartner
6 : to make nervous, tense, or excited usually used with up was too keyed up to sleep
7 : to enter or input (text or data) by using a keyboard keying changes to a manuscript often used with in or into key in a passwordinformation being keyed into a database
8 : to be essential to : play the most important part in defense keyed the victory
9 : to vandalize by scratching with a key someone keyed my car door

intransitive verb

1 : to use a key
2 : to observe the position or movement of an opposing player in football in order to anticipate the play usually used with on The middle linebacker was keying on the halfback.
3 : to operate a machine by means of a keyboard : keyboard


noun (2)

Definition of key (Entry 4 of 5)

: a low island or reef specifically : any of the coral islets off the southern coast of Florida the Florida Keys


noun (3)

Definition of key (Entry 5 of 5)

: a kilogram especially of marijuana or heroin

Other Words from key

Noun (1)

keyed \ ˈkēd How to pronounce key (audio) \ adjective
keyless \ ˈkē-​ləs How to pronounce key (audio) \ adjective

Examples of key in a Sentence

Adjective He's a key player in the organization. The key question is “Can we afford it?”. Underline key words and phrases as you read. Their votes were key in getting the bill passed. Verb The changes to the manuscript are being keyed by the typist. her response was perfectly keyed to the situation See More

First Known Use of key

Noun (1)

before the 12th century, in the meaning defined at sense 1a


1832, in the meaning defined above


14th century, in the meaning defined at transitive sense 1

Noun (2)

1693, in the meaning defined above

Noun (3)

1966, in the meaning defined above

History and Etymology for key

Noun (1), Adjective, and Verb

Middle English, from Old English cǣg; akin to Old Frisian kēi key

Noun (2)

Spanish cayo, from Taino

Noun (3)

by shortening & alteration from kilo

Buying Guide

Protect your home with smart door locks selected by our Reviews team.

Learn More About key

Time Traveler for key

Time Traveler

The first known use of key was before the 12th century

See more words from the same century

Dictionary Entries Near key




See More Nearby Entries 

Statistics for key

Cite this Entry

“Key.” Dictionary, Merriam-Webster, Accessed 8 Aug. 2022.

Style: MLA
MLACheck Mark Icon ChicagoCheck Mark Icon APACheck Mark Icon Merriam-WebsterCheck Mark Icon

More Definitions for key


\ ˈkē How to pronounce key (audio) \

Kids Definition of key

 (Entry 1 of 4)

1 : an instrument by which the bolt of a lock (as on a door) is turned or by which an engine is started
2 : a device having the form or function of a key Can you wind the clock with the key?
3 : the thing that is necessary or most important in doing something To learn a skill, practice is the key.
4 : something (as a map legend) that gives an explanation : solution
5 : one of the levers with a flat surface that is pressed with a finger to activate a mechanism of a machine or instrument computer keys
6 : a system of seven musical tones arranged in relation to a keynote from which the system is named the key of C


keyed; keying

Kids Definition of key (Entry 2 of 4)

1 : to regulate the musical pitch of
2 : to bring into harmony
3 : to record or enter by operating the keys of a machine The cashier keyed in the price.



Kids Definition of key (Entry 3 of 4)

: of great importance : most important She is one of our key players.



Kids Definition of key (Entry 4 of 4)

: a low island or reef the Florida Keys



Legal Definition of key

: of vital importance (as in a business organization) especially so as to be specially insured to the benefit of an employer key man key employee insurance

Key biographical name (1)

\ ˈkē How to pronounce Key (audio) \

Definition of Key

 (Entry 1 of 2)

Francis Scott 1779–1843 American lawyer and author of "The Star-Spangled Banner"


biographical name (2)

Definition of Key (Entry 2 of 2)

John (Phillip) 1961–     prime minister of New Zealand (2008–16)

More from Merriam-Webster on key

Nglish: Translation of key for Spanish Speakers

Britannica English: Translation of key for Arabic Speakers Encyclopedia article about key


Test Your Vocabulary

The Great British Vocabulary Quiz

  • union jack speech bubble
  • Named after Sir Robert Peel, what are British police called?
True or False

Test your knowledge - and maybe learn something along the way.

Universal Daily Crossword

A daily challenge for crossword fanatics.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!