Monday is the Moon's day in most European languages — lundi, lunedì, lunes, Montag — and in Sanskrit too, where Somavara means the same thing.

The seven-day week with planetary names spread from Hellenistic Egypt and reached India independently enough that the correspondences still match: Sunday the Sun, Monday the Moon, and so on down the classical order. In Vedic remedial practice Monday is when you fast for the Moon and wear the pearl for the first time, which is the same idea arriving from the other direction.