—key /kiː/
adjective
► B2 very important and having a lot of influence on other people or things: » She was a key figure in the international art world.» a key factor in tackling the problemThesaurus+: ↑Very important or urgent• • •
Extra Examples:» I think there is one key fact that you have overlooked.» The key witness for the prosecution was offered police protection after she received death threats.» The control of inflation is a key component of the government's economic policy.» Delegation of responsibility is a key part of a manager's job.» The economy is regarded as the key factor which will determine the outcome of the general election.noun [C] (ANSWERS)
► A2 a list of the answers to the questions in an exercise or test: » See the key to test 3 on page 176.noun [C] (LOCK)
► A1 a piece of metal that has been cut into a special shape and is used for opening or closing a lock, starting a car engine, etc.: » car/door keysSee picture: door key 
Thesaurus+: ↑Locks and locksmithing
• • •
Extra Examples:» She fumbled around in her handbag, looking for her key.» I heard someone turn a key in the lock.» Give me the car keys - you're in no fit state to drive.» She suddenly remembered (that) her keys were in her other bag.» Please hand in your keys at reception on your departure from the hotel.noun [C] (MUSICAL NOTES)
► F0 a set of musical notes based on one particular note: » The song changes key halfway through.» the key of C minorSee picture: key signature Thesaurus+: ↑Technical music terms
noun [C] (PART)
► B2 any of the set of moving parts that you press with your fingers on a computer keyboard, or musical instrument to produce letters, numbers, symbols, or musical notesSee picture: clarinet key See picture: keys
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Thesaurus+: ↑Machine parts
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Extra Examples:» If you press this key, the computer screen will clear .» Press and hold down the control key while you press '9'.» Press the return key twice to leave a blank line.» Use this key to toggle between the two typefaces.» He ran his fingers over the piano keys.noun [C] (SYMBOLS)
► F0 a list of the symbols used in a map or book with explanations of what they meanSee picture: map key Thesaurus+: ↑Maps and map-makingThesaurus+: ↑Signs, signals and symbols , ↑Specific signs and symbolsThesaurus+: ↑Reasons and explanations