So, as we all know, a key is used to lock or unlock a door, gate, or something else.  It’s either made of shiny metal, brass, or rusty iron, it can be small, or very, very big, as is the key to a dungeon.

We can have one key or we can have many or even a master key that unlocks everything, very handy if you have a house full of locked rooms.

People always seem to want to steal them, especially in crime shows.

There is also an item called a key card.  Not the metal thing, but a plastic thing, that opens doors.  Odd that it’s called keyless entry!

Then there’s what is known as the key to something, i.e. you might have the key to his or her heart, metaphorically speaking.

And in that metaphorical sense, it opens up pandora’s box with a plethora of different meanings.

He had the key to the puzzle.

I wish sometimes I had the key to be able to write better, that that one particular key eludes me.

There are keys on a keyboard, the ones you use on computers and calculators.  They were originally on typewriters.  You can also find keys on a piano, or an accordion, and some other musical instruments.

A key can also be a master index field, or unique identifier, in a database, particularly those kept on computers.

And,

there’s a host of other uses for the word key, such as

roughening a surface

describing the shooting area on a basketball court

a group, or one, of small coral islets

matching words to pictures

or, you’re just too keyed up to sleep.