This little word has a lot different meanings:

1. key (noun): used to unlock a door or car

2. key (noun): the individual piece on a keyboard, used for typing on a computer

3. key (noun): the black and white pieces played on a piano

4. key (noun): group of musical notes – “The song is played in the key of E minor.”

5. key (noun): sth. that provides meaning or gives understanding –  “The key to being a successful write is accepting that some of your work will be rejected.”

6. key (noun): a collection of symbols on a map or graph, telling you what the information means.

7. key (adjective): of great importance – “Martin Luther King Jr. was a key leader of the Civil Rights movement in the United States.”

8. under lock and key (idiom): in a protected place – “My mother keeps her jewelry under lock and key.” 

When you learn a new word, check your dictionary to see if it can be used in different ways.  It’s a very quick way to expand your vocabulary!