Athletes and the Sabbath

[BartholomewB]

But in this case, it’s just the name of the day … In classical Latin, I believe feria meant a holiday, a day when the law courts were closed and slaves had a rest day. But by the reign of Constantine, when the earliest records are found with these names for the days of the week, it looks as though there must have been a shift in meaning of some kind.

[Edit]
Just seen your edit about the meaning “weekday.” That’s the answer to the question, then!