星期天(xīng qī tiān) - Sunday in Mandarin

星期天 (xīngqī tiān) is Sunday, the other of the two Sunday words alongside 星期日 (xīngqī rì). Where 日 (rì) is the formal written character for "day", 天 (tiān) is the everyday spoken one, and 星期天 (xīngqī tiān) is what most Mandarin speakers actually say out loud.

Both words mean exactly the same thing and either is safe to use, but a learner who hears one spoken and one written on a calendar has not learned two different days - it is the same Sunday twice over.

星期天 (xīngqī tiān) rounds out the week: after 星期六 (xīngqī liù, "Saturday") comes 星期天 (xīngqī tiān), and then the numbering starts again at 星期一 (xīngqī yī, "Monday").