https://gizmodo.com/why-we-say-o-clock-1655979092I searched out the meaning of the contraction several months ago, but this was a bit more informative. The solar time versus the time on the clock are indeed going to vary depending on the season. Thought a few goats might appreciate this tidbit. An oft-used contraction and I've gone the vast majority of my life without knowing what it's short for.
