Monday – le lundi
Monday always used to be mundane because it was when we did the laundry (lundi), being the first day of work after the weekend.
Note: In French, the days of the week do NOT start with a capital letter.
The days of the week in French are all masculine, so it would be le lundi, le mardi, le mercredi, le jeudi, le vendredi, le samedi and le dimanche. However, in practice, the “le” is rarely used before the name of a day.
Imagine one of the early learner’s first lessons is the days of the week: