• (RP) enPR: kē, IPA: /kiː/
• (America) IPA: /ki/
• IPA: [kʲʰi̞i̯], [cʰi̞i̯]

From Middle English keye, kaye, keiȝe, from Old English cǣġ (whence also Scots key and kay ("key")), of uncertain origin.

key (plural keys)

1. An object designed to open and close a lock.
   • 1913, Joseph C[rosby] Lincoln, chapter XIII, in Mr. Pratt’s Patients, New York, N.Y., London: D[aniel] Appleton and Company, →OCLC ↗:

     We tiptoed into the house, up the stairs and along the hall into the room where the Professor had been spending so much of his time. 'Twas locked, of course, but the Deacon man got a big bunch of keys out of his pocket and commenced to putter with the lock.

2. An object designed to fit between two other objects (such as a shaft and a wheel) in a mechanism and maintain their relative orientation.
3. A crucial step or requirement.

   The key to solving this problem is persistence.

   the key to winning a game

   • a. 1705, John Locke, “Of the Conduct of the Understanding”, in Posthumous Works of Mr. John Locke: […], London: […] A[wnsham] and J[ohn] Churchill, […], published 1706, →OCLC ↗:

     Those who are accustomed to reason have got the true key of books.

   • 1850, [Alfred, Lord Tennyson], In Memoriam, London: Edward Moxon, […], →OCLC ↗, (please specify |part=Prologue or Rpilogue, or |canto=I to CXXIX):

     who keeps the keys of all the creeds

4. A guide explaining the symbols or terminology of a map or chart; a legend.

   The key says that A stands for the accounting department.

5. A guide to the correct answers of a worksheet or test.

   Some students cheated by using the answer key.

6. (computing) One of several small, usually square buttons on a typewriter or computer keyboard, mostly corresponding to text characters.

   Press the Escape key.

7. (music)
   1. In musical instruments, one of the valve levers used to select notes, such as a lever opening a hole on a woodwind.
   2. In instruments with a keyboard such as an organ or piano, one of the levers, or especially the exposed front end of it, which are depressed to cause a particular sound or note to be produced.
8. (music) A scale or group of pitches constituting the basis of a musical composition.

   the key of B-flat major

   • 1881, R.L. Stevenson, Virginibus Puerisque:

     A girl, it is true, has always lived in a glass house among reproving relatives, whose word was law; she has been bred up to sacrifice her judgments and take the key submissively from dear papa; and it is wonderful how swiftly she can change her tune into the husband's.

   1. The lowest note of a scale; keynote.
   2. In musical theory, the total melodic and harmonic relations, which exist between the tones of an ideal scale, major or minor; tonality.
   3. In musical theory and notation, the tonality centering in a given tone, or the several tones taken collectively, of a given scale, major or minor.
   4. In musical notation, a sign at the head of a staff indicating the musical key.
9. (figurative) The general pitch or tone of a sentence or utterance.
   • 1613–1614 (date written), John Fletcher, William Shak[e]speare, The Two Noble Kinsmen: […], London: […] Tho[mas] Cotes, for Iohn Waterson;  […], published 1634, →OCLC ↗, Act I, scene i, page 1 ↗:

     2. Queen. […] Deere Glasse of Ladies
     Bid him that we whom flaming war doth scortch,
     Vnder the shaddow of his Sword, may coole us:
     Require him he advance it ore our heades;
     Speak't in a womans key: like such a woman
     As any of us three; weepe ere you faile; lend us a knee;
     But touch the ground for us no longer time
     Then a Doves motion, when the head's pluckt off:
     Tell him if he i'th blood cizd field, lay swolne
     Showing the Sun his Teeth; grinning at the Moone
     What you would doe.

   • ?, William Cowper, Conversation

     You fall at once into a lower key.

10. (advertising) A modification of an advertisement so as to target a particular group or demographic.
    • 1998, Mail Order Success Secrets:

      Another popular way to key ads and mailings is to use a suite number, room number, department number, desk number, etc. as part of the ordering address. With a classified ad, using such a key may increase your ad cost.

11. (botany) An indehiscent, one-seeded fruit furnished with a wing, such as the fruit of the ash and maple; a samara.
12. (historical) A manual electrical switching device primarily used for the transmission of Morse code.
13. (cryptography) A piece of information (e.g., a password or passphrase) used to encode or decode a message or messages.
14. (internet) A password restricting access to an IRC channel.
15. (databases) In a relational database, a field used as an index into another table (not necessarily unique).
16. (computing) A value that uniquely identifies an entry in a container.
17. (basketball) The free-throw lane together with the circle surrounding the free-throw line, the free-throw lane having formerly been narrower, giving the area the shape of a skeleton key hole.

    He shoots from the top of the key.

18. (biology) A series of logically organized groups of discriminating information which aims to allow the user to correctly identify a taxon.
19. (architecture) A piece of wood used as a wedge.
20. (architecture) The last board of a floor when laid down.
21. (masonry) A keystone.
22. That part of the plastering which is forced through between the laths and holds the rest in place.
23. (rail transport) A wooden support for a rail on the bullhead rail system.
24. The degree of roughness, or retention ability of a surface to have applied a liquid such as paint, or glue.

    The door panel should be sanded down carefully to provide a good key for the new paint.

25. (cartomancy) The thirty-third card of the Lenormand deck.
26. (print and film) The black ink layer, especially in relation to the three color layers of cyan, magenta, and yellow. See also CMYK.
27. (computer graphics, television) A color to be masked or made transparent.
    • 2004, Mark Schmidt, Simon Robinson, Microsoft Visual C# .NET 2003 Developer's Cookbook, page 195:

      You can easily create this type of user interface by creating a bitmap with certain portions set to a predefined color you want to use as the transparency key.

• French: clé, clef
• German: Schlüssel
• Italian: chiave
• Portuguese: chave
• Russian: ключ
• Spanish: llave, llavín

• Russian: чека́
• Spanish: cuña

• French: clé, clef
• German: Schlüssel
• Italian: chiave, cruciale
• Portuguese: chave
• Russian: ключ
• Spanish: clave

• French: légende
• German: Zeichenerklärung, Legende
• Italian: legenda
• Portuguese: legenda
• Russian: леге́нда
• Spanish: clave, leyenda

• French: touche
• German: Taste
• Italian: tasto
• Portuguese: tecla
• Russian: кла́виша
• Spanish: tecla

• French: touche
• German: Taste
• Italian: tasto
• Portuguese: tecla
• Russian: кла́виша
• Spanish: tecla

• French: tonalité
• German: Tonart
• Italian: chiave
• Portuguese: clave
• Russian: тона́льность
• Spanish: clave

• German: Taste
• Italian: tasto telegrafico
• Russian: телеграфный ключ

• French: clé, clef
• German: Schlüssel
• Italian: chiave
• Portuguese: chave
• Russian: ключ
• Spanish: clave

• French: clé, clef
• German: Schlüssel
• Italian: chiave
• Portuguese: chave
• Russian: ключ
• Spanish: clave

• French: clé, clef
• German: Schlüssel
• Italian: chiave
• Portuguese: chave
• Russian: ключ
• Spanish: clave

• French: clé, clef
• German: Schlüssel
• Italian: chiave
• Portuguese: chave, índice
• Russian: ключ

• German: Zone
• Portuguese: garrafão

key

1. Indispensable, supremely important.

   He is the key player on his soccer team.

   • 2007, Mark H. Moss, Shopping as an Entertainment Experience, page 46:

     Lukas intimates that one of Disney's key attractions was "Main Street USA,” which "mimicked a downtown business district just as Southdale" had done.

2. Important, salient.

   She makes several key points.

• French: clé
• Italian: chiave, essenziale, indispensabile
• Portuguese: chave
• Russian: ключево́й
• Spanish: clave

• French: clé
• Italian: chiave
• Portuguese: chave
• Russian: ключево́й

key (keys, present participle keying; simple past and past participle keyed)

1. To fit (a lock) with a key.
2. To fit (pieces of a mechanical assembly) with a key to maintain the orientation between them.
3. To mark or indicate with a symbol indicating membership in a class.
   • 2007, Stephen Blake Mettee, Michelle Doland and Doris Hall, compilers, The American Directory of Writer's Guidelines, 6th ("2007–2008") edition, ISBN 1884956580, page 757,

     Indicate the comparative value of each heading by keying it with a number in pencil, in the left margin, as follows: […]

4. (telegraphy and radio telegraphy) To depress (a telegraph key).
5. (radio) To operate (the transmitter switch of a two-way radio).
6. (computing) (more usually to key in) To enter (information) by typing on a keyboard or keypad.

   Our instructor told us to key in our user IDs.

7. (colloquial) To vandalize (a car, etc.) by scratching with an implement such as a key.

   He keyed the car that had taken his parking spot.

8. To link (as one might do with a key or legend).
   • 1960, Richard L. Masland, “Classification of the Epilepsies”, in Epilepsia, volume 1, page 516:

     The American Heart Association has prepared their own guide to classification and, keying it with the Standard Nomenclature of Diseases, have done much to encourage a concise yet complete diagnosis.

9. (intransitive, biology, chiefly, taxonomy) To be identified as a certain taxon when using a key.
10. (advertising, transitive) To modify (an advertisement) so as to target a particular group or demographic.
    • 1936, John Freeman Pyle, Marketing Principles, Organization and Policies, page 711:

      Keying advertisements and counting the number of inquiries received or the number of coupons returned to indicate the "pulling power" of a particular piece of copy or the coverage of a particular advertising medium.

    • 1998, Mail Order Success Secrets:

      Another popular way to key ads and mailings is to use a suite number, room number, department number, desk number, etc. as part of the ordering address. With a classified ad, using such a key may increase your ad cost. Why? Because you're using an extra word or two to key the ad.

11. To attune to; to set at; to pitch.
    • 1930, Norman Lindsay, Redheap, Sydney, N.S.W.: Ure Smith, published 1965, →OCLC ↗, page 23:

      To Ethel alone she addressed a stray remark, keyed below the sound of other voices.

12. To fasten or secure firmly; to fasten or tighten with keys or wedges.
13. To prepare for plastering by adding the key that part of the plastering which is forced through between the laths and holds the rest in place.
14. To provide an arch with a keystone.
15. Clipping of chromakey.

• Portuguese: digitar, teclar
• Russian: вводи́ть
• Spanish: teclear

• Portuguese: riscar

Variant of cay, from Spanish cayo, from tnq cayo

key (plural keys)

1. One of a string of small islands.

   the Florida Keys

• French: caye
• Spanish: cayo

key (plural keys)

1. (slang) A kilogram, especially of a recreational drug.

   Synonyms: kay

   • 2010, David J. Silas, Da Block, page 41:

     So starting with ten keys of cocaine and two keys of heroin, Derrick put his plan in motion. Soon every major drug dealer and gang chief from Chicago Avenue to Evanston was in his pocket.

key (plural keys)

1. Alternative form of quay

1. Surname.