ball · noun C /bɔːl/
ball
A1 a round object that you throw, kick, or hit in a game, or something with this shape
Dictionary examples:
a beach/golf/tennis ball
She threw a ball at me and I caught it.
Just try to concentrate on hitting/kicking the ball.
a ball of wool
The kitten curled itself into a ball.
Learner example:
They gave me a ball and a T-shirt. (Key English Test; A2; Portuguese)
be on the ball
C1 to be quick to understand and react to things
Dictionary example:
She's over ninety, but she's still on the ball.
Learner example:
When you're at Sants station, you'll need to be on the ball. (Certificate in Advanced English; C1; Spanish)
get/start the ball rolling
C2 to make something begin or happen
Dictionary example:
We have to get the ball rolling on this project soon.
