noun

• (countable) An object designed to open and close a lock.
  "We tiptoed into the house, up the stairs and along the hall into the room where the Professor had been spending so much of his time. 'Twas locked, of course, but the Deacon man got a big bunch of keys out of his pocket and commenced to putter with the lock."
• (computing) One of several small, usually square buttons on a typewriter or computer keyboard, mostly corresponding to text characters.
  "Press the Escape key."
• (music)
• (music)

verb

• (telegraphy and radio telegraphy) To depress (a telegraph key).
• (radio) To operate (the transmitter switch of a two-way radio).
• (computing) (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."
• (colloquial) To vandalize (a car, etc.) by scratching with an implement such as a key.
  "He keyed the car that had taken his parking spot."

noun

• (slang) A kilogram, especially of a recreational drug.
  "So starting with ten keys of cocaine and two keys of heroin, Derrick put his plan in motion. Soon every major drug dealer and gang chief from Chicago Avenue to Evanston was in his pocket."