time ball
/taɪm bɔl/
noun
- A large ball that drops at a set time each day, used historically to help ships and people set their clocks accurately.
- Sailors used to watch the time-ball to check their marine chronometers.
- In the 19th century, many ports had a time-ball that signaled the correct time to ships in the harbor.
- The time-ball at the Greenwich Observatory drops at exactly 1:00 PM every day.