What it means

1. noun United States writer best known for his autobiographical works (1874-1935)
2. noun a period of opportunity
   “he deserves his day in court”
3. noun some point or period in time
   “it should arrive any day now”
4. noun the recurring hours when you are not sleeping (especially those when you are working)
   “my day began early this morning”
5. noun time for Earth to make a complete rotation on its axis
   “two days later they left”
6. noun a day assigned to a particular purpose or observance
   “Mother's Day”
7. noun the time after sunrise and before sunset while it is light outside
   “the dawn turned night into day”
8. noun the period of time taken by a particular planet (e.g. Mars) to make a complete rotation on its axis
   “how long is a day on Jupiter?”
9. noun an era of existence or influence
   “in the day of the dinosaurs”
10. noun the time for one complete rotation of the earth relative to a particular star, about 4 minutes shorter than a mean solar day