big day—a day on which important things happen:
- Today is going to be a big day for local athletes.
1. a working-day of fairly lengthy duration:
- I made a very long day last Friday.
2. a day perceived as lasting unusually long (because it is boring, etc.):
- I was held up by storms for three long days.
3. (biol.) a long period of light:
- In most polycyclic insects long days cause continuous development.