Key

The word key has several uses: {{wiktionary}}

Instrument or Tool

• A key (instrument) comprises a moving part of a musical instrument.
• A key (cryptography) consists of a piece of information, usually kept secret, used to customise ciphers.
• A key (lock) as a physical object (tool) used to manipulate a lock.
• A key plate in printing refers to the printing plate which impressed the artistic detail of an image.
• A skate key functions as a tool in the adjusting of roller skates.
• A telegraph key serves to send Morse code.
• Typewriters and computer keyboards have buttons called keys used for the input of text or commands.