nine o'clock
noun1
The start of the tenth hour of the day; 9:00 a.m. (09:00).
In both the 12-hour clock and the 24-hour clock
- The breakfast buffet opens at nine o'clock (= "The breakfast buffet opens at 9:00 a.m.").
2
The start of the twenty-second hour of the day; 9:00 p.m. (21:00).
Only in the 12-hour clock
- Supper was served at nine o'clock (= "Supper was served at 9:00 p.m.").
3
Informal To the left (horizontal clock orientation) (from the location of the 9 mark on a clock face)
- We've got a bogey at nine o'clock.