1Sunday, typically the first or last day of the week, following Saturday — commonly a day off for many people.
日曜日はいつも家族と過ごす。
I always spend Sundays with my family.
今度の日曜日、一緒に買い物に行きませんか。
Would you like to go shopping together this Sunday?
日曜日の朝はゆっくり寝ていたい。
On Sunday mornings I like to sleep in.
郵便局は日曜日は休みだ。
The post office is closed on Sundays.