key1
  
  n.
 (pl. keys)
         - a small piece of shaped metal with incisions cut to fit the wards of a particular lock, which is inserted into the lock and rotated to open or close it or to operate a switch. ▸an instrument for grasping and turning a screw, peg, or nut. ▸a pin, bolt, or wedge inserted into a hole or between parts so as to lock the parts together. 
- a lever depressed by the finger in playing an instrument such as the organ, piano, flute, or concertina.
- each of several buttons on a panel for operating a typewriter, word processor, or computer terminal.
- a lever operating a mechanical device for making or breaking an electric circuit.
- a thing that provides access to or understanding of something:![]()  a key to success. ▸an explanatory list of symbols used in a map or table. ▸a set of answers to exercises or problems. ▸a word or system for solving a cipher or code. ▸the first move in the solution of a chess problem. 
- Music  a group of notes based on a particular note and comprising a scale, regarded as forming the tonal basis of a passage of music. ▸the tone or pitch of someone's voice. 
- the dry winged fruit of an ash, maple, or sycamore; a samara.
- roughness on a surface, provided to assist adhesion of plaster or other material.
- Basketball  the keyhole-shaped area marked on the court near each basket.
adj.
 of crucial importance:
![]() 
 a key figure.
v.
 (keys, keying, keyed)
     - enter or operate on (data) by means of a computer keyboard.
- fasten into position with a pin, wedge, or bolt.
- 
(key to)
 chiefly N. Amer. link with. ▸
(key into/in with)
 be connected or in harmony with. 
- 
(be keyed up)
 be nervous, tense, or excited.
- roughen (a surface) to assist adhesion of plaster or other material.
Phrase
  
    
      - in 
(or out of)
 key
 in (or out of) harmony.
 
  Derivative
  
    - keyed adj.
- keyer n.
- keyless adj.
 
  Etymology
  OE cæg, cæge, of unknown origin.
 
  
    
key2
  
  n.
 a low-lying island or reef, especially off the coast of Florida or in the Caribbean.
Etymology
  C17: from Sp. cayo ‘reef’, influenced by quay.