A1 a period of 24 hours: the days of the week I saw her the day before yesterday.
A2 the period during the day when there is light from the sun: a bright, sunny day
A2 the time that you usually spend at work or school: It’s been a very busy day at the office. I have a day off (= when I am not at work) tomorrow.
one day A2 used to talk about something that happened in the past: One day, I came home to find my windows smashed.
these days A2 used to talk about the present period of time: I don’t go out much these days.
for days B1 for a long time: I haven’t seen Jack for days.
one day/one of these days B1 used to talk about something you think will happen in the future: One of these days I’ll tell her what really happened.
the other day B1 a few days ago: I saw Terry in the bank the other day.
day after day › every day for a long period of time: Day after day they marched through the mountains.