O'clock
来自Big Physics
late Middle English: from Middle Low German and Middle Dutch klocke, based on medieval Latin clocca ‘bell’.
wiktionary
Shortened form of of the clock.
etymonline
o'clock (adj.)
phrase preceded by one, two, three, etc., and signifying the time of day as shown by the face of a clock, c. 1720, an abbreviation of of the clock, from Middle English of the clokke (late 14c.). See O + clock (n.). The use of clock hand positions to describe vector directions or angles is from late 18c.
