cork

A cork is a small, round piece of wood which people put in the top of a bottle to close it.

Example: I took the cork out of the wine bottle with a corkscrew.

Cork is a type of wood. It is quite soft and light. It is often used to make corks (sense 1).

If you cork a bottle, you seal it with a cork.

If you cork something, you blacken it with a burnt cork.