one/two/three, etc. o'clock
A1
used after the numbers one to twelve to mean exactly that hour when you tell the time
Dictionary examples:
My boss smiles at one o'clock. (0.0)
The bus is late at nine o'clock. (0.0)
My stomach growls at twelve o'clock. (0.0)
It was ten o'clock when we got home. (20.8)