Meaning ofo'clockin English

Adverb

1. at a specific hour; exactly on time
   The meeting starts at 9 o'clock.
2. specifying the hour of day
   The train arrives at 5 o'clock every morning.
3. referring to a usual or routine time
   We usually have lunch at 12 o'clock.
4. indicating daily event timing
   The store closes at 6 o'clock sharp.