Sunday — the day of the week, often used as a day off or part of the weekend.
日曜日は友達と映画を見に行く予定だ。
I'm planning to go see a movie with friends on Sunday.
日曜日は店が休みのところが多い。
Many shops are closed on Sundays.
毎週日曜日に家族で食事をするのが習慣だ。
It's a habit for my family to have a meal together every Sunday.