noun, plural keys.

  1. a small metal instrument specially cut to fit into a lock and move its bolt.
  2. any of various devices resembling or functioning as a key: the key of a clock.
  3. key card.
  4. something that affords a means of access: the key to happiness.
  5. something that secures or controls entrance to a place: Gibraltar is the key to the Mediterranean.
  6. something that affords a means of clarifying a problem.
  7. a book, pamphlet, or other text containing the solutions or translations of material given elsewhere, as testing exercises.
  8. a systematic explanation of abbreviations, symbols, etc., used in a dictionary, map, etc.: pronunciation key.Compare legend(def 4).
  9. the system, method, pattern, etc., used to decode or decipher a cryptogram, as a code book, machine setting, or keyword.
  10. one of a set of marked parts, designated areas, or levers pressed in operating a typewriter, computer terminal, calculator, etc.
  11. a manually operated lever for opening and closing an electric circuit, used to produce signals in telegraphy.
  12. Music.
    1. (in a keyboard instrument) one of the levers that when depressed by the performer sets in motion the playing mechanism.
    2. (on a woodwind instrument) a metal lever that opens and closes a vent.
    3. the relationship perceived between all tones in a given unit of music and a single tone or a keynote; tonality.
    4. the principal tonality of a composition: a symphony in the key of C minor.
    5. the keynote or tonic of a scale.
  13. tone or pitch, as of voice: to speak in a high key.
  14. mood or characteristic style, as of expression or thought: He writes in a melancholy key.
  15. degree of intensity, as of feeling or action.
  16. a pin, bolt, wedge, or other piece inserted in a hole or space to lock or hold parts of a mechanism or structure together; a cotter.
  17. a small piece of steel fitting into matching slots of a hub of a wheel or the like and the shaft on which the wheel is mounted so that torque is transmitted from one to the other.
  18. a contrivance for grasping and turning a bolt, nut, etc.
  19. Computers. a field or group of characters within a record that identifies the record, establishing its position among sorted records, and/or provides information about its contents.
  20. (in a series of advertisements or announcements soliciting replies) a unique code inserted for each medium used, to determine the relative effectiveness of the media.
  21. Electricity.
    1. a device for opening and closing electrical contacts.
    2. a hand-operated switching device ordinarily formed of concealed spring contacts with an exposed handle or push button, capable of switching one or more parts of a circuit.
  22. Biology. a systematic tabular classification of the significant characteristics of the members of a group of organisms to facilitate identification and comparison.
  23. Masonry. a keystone.
  24. Architecture. (in a ribbed vault) a stone, as a boss, at the intersection of two or more ribs.
  25. Masonry, Carpentry. a wedge, as for tightening a joint or splitting a stone or timber.
  26. Carpentry. a small piece of wood set into a timber across the grain to prevent warping.
  27. Building Trades. any grooving or roughness applied to a surface to improve its bond with another surface.
  28. Basketball. keyhole(def 2).
  29. Photography. the dominant tonal value of a picture, a high-key picture having light tonal values and minimal contrast and a low-key picture being generally dark with minimal contrast.
  30. Painting. the tonal value and intensity of a color or range of colors: Rembrandt’s colors are characterized by their low key.
  31. Botany. a samara.
  32. (initial capital letter) a member of the House of Keys.
  33. keys, spiritual authority.


  1. chief; major; important; essential; fundamental; pivotal: a key person in the company; key industries.

verb (used with object), keyed, key·ing.

  1. to regulate or adjust (actions, thoughts, speech, etc.) to a particular state or activity; bring into conformity: to key one’s speech to the intellectual level of the audience.
  2. Music. to regulate the key or pitch of.
  3. Painting.
    1. to paint (a picture) in a given key.
    2. to adjust the colors in (a painting) to a particular hue: He keyed the painting to brown.
  4. to fasten, secure, or adjust with a key, wedge, or the like, as parts of a mechanism.
  5. to provide with a key.
  6. (in the layout of newspapers, magazines, etc.) to identify, through signs or symbols, the positions of illustrations or pieces of copy in a dummy.
  7. to lock with or as if with a key.
  8. Masonry. to provide (an arch or vault) with a keystone.
  9. Computers. keyboard(def 4).

verb (used without object), keyed, key·ing.

  1. to use a key.
  2. Computers. keyboard(def 4).

Verb Phrases

  1. key in, Computers. keyboard(def 4).
  2. key on,
    1. watch the position and movements of an opponent in order to anticipate a play: The defensive backs keyed on the star receiver.
    2. Also key in single out as of prime importance or interest; be intent on or obsessed with: a company that is keyed in on growth.
  3. key up,
    1. to bring to a particular degree of intensity of feeling, excitement, energy, nervousness, agitation, etc.: keyed up over the impending test.
    2. to raise (a piece of masonry) by the insertion of a wedge or wedges.
    3. to raise (the haunches of an arch) by the insertion of a voussoir.

  1. power of the keys, the authority of a pope in ecclesiastical matters, vested in him as successor of St. Peter.

noun, plural keys.

  1. a reef or low island; cay.

noun, plural keys. Slang.

  1. a kilogram of marijuana or a narcotic drug.


  1. Scot dialect a children’s cry for truce or respite from the rules of a game


  1. a metal instrument, usually of a specifically contoured shape, that is made to fit a lock and, when rotated, operates the lock’s mechanism
  2. any instrument that is rotated to operate a valve, clock winding mechanism, etc
  3. a small metal peg or wedge inserted into keyways
  4. any of a set of levers operating a typewriter, computer, etc
  5. any of the visible parts of the lever mechanism of a musical keyboard instrument that when depressed set in motion the action that causes the instrument to sound
    1. Also called: tonalityany of the 24 major and minor diatonic scales considered as a corpus of notes upon which a piece of music draws for its tonal framework
    2. the main tonal centre in an extended compositiona symphony in the key of F major
    3. the tonic of a major or minor scale
    4. See tuning key
  6. something that is crucial in providing an explanation or interpretationthe key to adult behaviour lies in childhood
  7. a means of achieving a desired endthe key to happiness
  8. a means of access or controlGibraltar is the key to the Mediterranean
  9. a list of explanations of symbols, codes, etc
  10. a text that explains or gives information about a work of literature, art, or music
  11. Also called: key move the correct initial move in the solution of a set problem
  12. biology a systematic list of taxonomic characteristics, used to identify animals or plants
  13. photog painting the dominant tonal value and colour intensity of a pictureSee also low-key (def. 3), high-key
  14. electrical engineering
    1. a hand-operated device for opening or closing a circuit or for switching circuits
    2. a hand-operated switch that is pressed to transmit coded signals, esp Morse code
  15. the grooving or scratching of a surface or the application of a rough coat of plaster, etc, to provide a bond for a subsequent finish
  16. pitchhe spoke in a low key
  17. a characteristic mood or stylea poem in a melancholic key
  18. level of intensityshe worked herself up to a high key
  19. railways a wooden wedge placed between a rail and a chair to keep the rail firmly in place
  20. a wedge for tightening a joint or for splitting stone or timber
  21. short for keystone (def. 1)
  22. botany any dry winged fruit, esp that of the ash
  23. (modifier) photog determining the tonal value of a photographflesh colour is an important key tone


  1. of great importance; cruciala key issue

verb (mainly tr)

  1. (foll by to) to harmonize (with)to key one’s actions to the prevailing mood
  2. to adjust or fasten with a key or some similar device
  3. to provide with a key or keys
  4. to scratch the paintwork of (a car) with a key
  5. (often foll by up) to locate the position of (a piece of copy, artwork, etc) on a layout by the use of symbols
  6. (also intr) another word for keyboard (def. 3)
  7. to include a distinguishing device in (an advertisement, etc), so that responses to it can be identified
  8. to provide a keystone for (an arch)


  1. a variant spelling of cay


  1. John (Phillip). born 1961, New Zealand politician; prime minister from 2008

“metal piece that works a lock,” from Old English cæg “key,” of unknown origin, with no certain cognates other than Old Frisian kei. Perhaps related to Middle Low German keie “lance, spear” on notion of “tool to cleave with,” from Proto-Germanic *ki- “to cleaver, split” (cf. German Keil “wedge,” Gothic us-kijans “come forth,” said of seed sprouts, keinan “to germinate”). But Liberman writes, “The original meaning of *kaig-jo- was presumably ‘*pin with a twisted end.’ Words with the root *kai- followed by a consonant meaning ‘crooked, bent; twisted’ are common only in the North Germanic languages.” Modern pronunciation is a northern variant predominating from c.1700; earlier it was often spelled and pronounced kay.

Figurative sense of “that which serves to open or explain” was in Old English; meaning “that which holds together other parts” is from 1520s. As “answer to a test,” it is from chess, short for key move, “first move in a solution to a set problem.” Musical sense of “tone, note” is 15c., but modern sense of “scale” is 1580s, probably as a translation of Latin clavis or French clef (see clef; also cf. keynote). Extended c.1500 to “mechanism on a musical instrument.” As a verb meaning “to scratch (a car’s paint job) with a key” it is recorded by 1986.


“low island,” 1690s, from Spanish cayo “shoal, reef,” from Taino cayo “small island;” spelling influenced by Middle English key “wharf” (c.1300), from Old French kai “sand bank” (see quay).

  1. See cay.

The main or central note of a piece of music (or part of a piece of music). Each key has its own scale, beginning and ending on the note that defines the octave of the next scale. The key of C-major uses a scale that starts on C and uses only the white keys of the piano. In a piece composed in the key of C, the music is likely to end on the note C, and certain combinations of notes based on C will predominate.

In addition to the idiom beginning with key

  • key up

also see:

  • in key
  • under lock and key

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