nycti-, nyct-, nycto-, nyc- +

A period of darkness; a dark phase in a light/dark cycle.

An orientation response occurring at night or turning in a certain direction at night; nyctitropic, nyctitropism.

The tendency of certain plant organs, as the leaflets of clover, to assume special “sleeping” positions at night.

A device invented by Lewis Carroll with which one can record one’s ideas at night, in the dark, or when not fully awake.

Night blindness; failure or imperfection of vision at night or in a dim light, with good vision only on bright days.

1. In biology, a preference for the dark or for night.
2. An abnormal preference for darkness or night.

Someone who has an irrational fear of the dark.

An elective mutism with the loss of one's voice during the day but not at night.

The inability to see well at night.

Frequent urination during the night; especially, the passage of more urine at night than during the day; nocturia.

The Greek goddess of night, known to the Romans as Nox, was born, together with Erebus (Darkness), Ge (Earth), Tartarus, and Eros (Love), out of Chaos. With Erebus, she bore Aether (Upper Air) and Hemera (Day). She alone spawned a large brood that included Moros (Doom), Thanatos (Death), Hypnos (Sleep), the Fates, and Nemesis.

Nyx lived in Tartarus, from which she went forth each day just as Hemera was returning. Her only other recorded act was to save her son Hypnos when Zeus was about to throw him out of the realm of the gods.

Tartarus, by the way, was a dark region beneath the earth, and the personification of that region. Tartarus was said to be as far beneath Hades, or beneath the surface of the earth, as heaven was above it. Supposedly, an anvil would fall for nine days to reach it from earth’s surface.