Definition of "Day" :
noun: United States writer best known for his autobiographical works (1874-1935)
noun: a period of opportunity
"He deserves his day in court."
noun: some point or period in time
"It should arrive any day now."
noun: the recurring hours when you are not sleeping (especially those when you are working)
"My day began early this morning."
noun: time for Earth to make a complete rotation on its axis
"Two days later they left."
noun: a day assigned to a particular purpose or observance
noun: the time after sunrise and before sunset while it is light outside
"The dawn turned night into day."
noun: the time for one complete rotation of the earth relative to a particular star, about 4 minutes shorter than a mean solar day
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?."
noun: an era of existence or influence
"In the day of the dinosaurs."