Why do we call a large timepiece a "clock"?
Like cloche in French, clock literally means bell. When the large mechanical clock was invented in the 14th century it didn't tell time with a face and hands, but rather by sounding bells on the hour and then eventually on the quarter and half-hour. This time device was called a "clock" because it told time by sounding bells. O'clock, as in 12 o'clock etc., is an abbreviation for "of the clock" or "of the bells".