Some idioms with "day"

All day long = continuously e.g. We had awful weather. It rained all day long.
Any day now = soon e.g. The results will be coming out any day now.
Day in day out = continuously for several days e.g. My job is boring and monotonous. I do the same tasks day in day out.
One of these days = in the future e.g. One of these days, I’m sure we’ll catch the biggest fish in the river.

Good old days = to remember the past with fondness e.g. Do you remember the good old days when vegetables were fresh.
Make a day of it = spend all day doing something enjoyable e.g. We don’t often get to spend the weekend in the countryside, so we had better make a day of it.
Make somebody’s day = give somebody a welcome surprise e.g. When I went to work, all the filing was done. It really made my day.
Not to have all day = limited time e.g. Hurry up! I don’t have all day.
Off-day = when things go wrong e.g. He was having one of those off-days. The car broke down, it was raining and his bag was stolen.
Old days = distant past e.g. There weren’t any computers in the old days.
Save the day = prevent a failure e.g. The technician was able to fix the problem and so saved the day.
The other day = recently e.g. Did you watch the film the other day.
To have seen better days = outlived its usefulness e.g. Your shoes look worn out. They’ve seen better days.
That will be the day! = very unlikely e.g. That will be the day! He never comes to work on time!
At the end of the day = finally e.g. At the end of the day, you can always do the exam again.
Call it a day = bring to an end e.g. We are all tired. We’ve been working for hours. Let’s call it a day.
Early days = too soon to be sure e.g. The operation seemed to have gone well but it’s early days.
Have a field day = happy doing something e.g. The children had a field day painting the classroom.
Tomorrow is another day = there will be another opportunity e.g. Don’t worry about it. Tomorrow is another day. There are plenty of opportunities