Etymology 1

Noun

1. An object designed to open and close a lock.
2. An object designed to fit between two other objects (such as a shaft and a wheel) in a mechanism and maintain the orientation between them.
3. A crucial step or requirement.

   the key to solving this problem...

   the key to winning this game

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. One of several small, usually square buttons on a typewriter or computer keyboard, most of which generally correspond to a particular character.

   Press the Escape key.

6. One of a number of rectangular moving parts on a piano or musical keyboard, each causing a particular sound or note to be produced.
7. One of various levers on a musical instrument used to select notes, such as a lever opening a hole on a woodwind.
8. A hierarchical scale of musical notes on which a composition is based

   the key of B-flat major

9. A device used to transmit Morse code.
10. A piece of information (e.g. a passphrase) used to encode or decode a message or messages.
11. : In a relational database, a field used as an index into another table (not necessarily unique).
12. : A value that uniquely identifies an entry in an associative array.
13. : 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.

14. : kilogram

Adjective

1. Indispensable.

   He is the key player for his soccer team.

   He is the key witness.

2. Important, salient.

   She makes several key points

Verb

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. (telegraphy and radio telegraphy) To depress (a telegraph key).
4. (radio) To operate (the transmitter switch of a two-way radio).
5. : (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.

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

   He keyed the car that had taken his parking spot.

7. To link (as one might do with a key or legend).

   He hadn't keyed smoking with lung cancer.

   • 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.

8. To mark or indicate with a symbol indicating membership in a class.
   • 1996 January, Garden Dsign Ideas, second printing, Taunton Press, ISBN 1561580791, page 25,

     So I worked on a tissue-paper copy of the perimeter plan, outlining groupings of plants of the same species and keying them with letters for the species.

   • 2001, Bruce M. Metzger, The Bible in Translation, ISBN 0801022827, page 87,

     The volume closes with thirty pages of "Notes, critical and explanatory," in which Thomson provides seventy-six longer or shorter notes keyed to specific sections of the synopsis.

   • 2002, Karen Bromley, Stretching Students' Vocabulary, ISBN 0439288398, page 12,

     Talk about similarities between the words and write them below to the left of the anchor, keying them with a plus sign (+). Talk about the characteristics that set the words apart and list them below the box to the right, keying them with a tilde sign (~).

   • 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: