Today my Inquizitive Mind sat thinking that why do we add “o’clock” suffix to the time and not simply say the time.
This practice of saying “o’clock” comes from the ancient times when the clocks weren’t prevalent. The people used to refer to time by a variety of means, depending on their reference point.
As we all know, human civilization started recognizing time with the help of the sun. A day used, to begin with, sunrise and end with sunset. Soon people came up with the idea of the sundial to divide time. That being said solar time is different from a clock time. The clocks divide the time evenly into standard seconds, minutes and hours, but hour lengths in solar clocks vary due to seasonality.
Thus people started using “of the clock” as a suffix in the early 14th century to distinguish the fact that they were referring the “clock” and not the solar clock. They would say something like “eight of the clock” which shortened down to “eight o’clock” by the 17th and 18th centuries. Due to their habit of using slang everywhere, people dropped the “o” altogether in those centuries and started saying just “eight clock”.
The use of form “o’clock” again gained popularity in the 18th century when it became common to do a similar slurring of names. “Will of the wisp” became “Will-o’-the-wisp” (originating from a legend of an evil blacksmith named Will Smith, with “wisp” meaning “torch”). Similarly “Jack of the Lantern” became “Jack-o’-Lantern” which meant “Man of the Lantern” with “Jack” being generic for “any man”.
Now that clocks are pervasive people don’t really say “o’clock” to distinguish it from the solar clock. Anyway, you wouldn’t find any people referring the sun dial to follow time. The reference has been changed to the clock but the practice of saying “o’clock” has stuck over time.