night

Night is the dark period between sunset and sunrise.

(noun)

The hours between around 7 or 8 PM and 5 or 6 AM are an example of night.

See night in Webster's New World College Dictionary

noun

1. the period from sunset to sunrise
2. the period of actual darkness after sunset and before sunrise; also, a part of this period before bedtime [a night at the opera] or the part between bedtime and morning [a sleepless night]
the evening following a specified day: Christmas night
the darkness of night
any period or condition of darkness or gloom; specif.,
1. a period of intellectual or moral degeneration
2. a time of grief
3. death

Origin: ME niht < OE, akin to Ger nacht < IE base *nekwt-, *nokwt- > Gr nyx (gen. nyktos), L nox (gen. noctis), night

adjective

See night in American Heritage Dictionary 4

noun

a. The period between sunset and sunrise, especially the hours of darkness.
b. This period considered as a unit of time: for two nights running.
c. This period considered from its conditions: a rainy night.
The period between dusk and midnight of a given day: either late Thursday night or early Friday morning.
a. The period between evening and bedtime.
b. This period considered from its activities: a night at the opera.
c. This period set aside for a specific purpose: Parents' Night at school.
a. The period between bedtime and morning: spent the night at a motel.
b. One's sleep during this period: had a restless night.
Nightfall: worked from morning to night.
Darkness: vanished into the night.
a. A time or condition of gloom, obscurity, ignorance, or despair: “In a real dark night of the soul it is always three o'clock in the morning” (F. Scott Fitzgerald).
b. A time or condition marked by absence of moral or ethical values: “He never would have let us go untroubled into the night of private greed” (Anthony Lewis).