This is the 501st most frequent Italian word.
martedì
Tuesday.
In this sentence, 'martedì' is singular and refers directly to the day Tuesday of the week.
Martedì sono andato al mercato.
On Tuesday, I went to the market.
Here, 'martedì' is used with 'prossimo' to specify the upcoming Tuesday.
Ci vediamo martedì prossimo alle otto.
See you next Tuesday at eight o'clock.
In this case, 'martedì' is plural, 'i martedì', conveying a habitual action occurring on Tuesdays.