n.1. The period of light between dawn and nightfall; the interval from sunrise to sunset.
2. a. The 24-hour period during which the earth completes one rotation on its axis, traditionally measured from midnight to midnight.
b. The period during which a celestial body makes a similar rotation.
3. One of the numbered 24-hour periods into which a week, month, or year is divided.
4. The portion of a 24-hour period that is devoted to work, school, or business: an eight-hour day; a sale that lasted for three days.
5. A 24-hour period or a portion of it that is reserved for a certain activity: a day of rest.
6. a. A specific, characteristic period in one's lifetime: In Grandmother's day, skirts were long.
b. A period of opportunity or prominence: Every defendant is entitled to a day in court. That child will have her day.
7. A period of time in history; an era: We studied the tactics used in Napoleon's day. The day of computer science is well upon us.
8. days Period of life or activity: The sick cat's days will soon be over.
adj.1. Of or relating to the day.
2. Working during the day: the day nurse.
3. Occurring before nightfall: a day hike.