When the sun goes down.

Evening refers to the time when the sun sets; Good evening.

Generally speaking, at night.

Evening generally refers to night.

Pictographs of the moon

In Oracle Bone Inscriptions, "Xi" and "Moon" are the same word, and both are hieroglyphics of half a moon.

Evening, dusk

The original meaning of the word "Xi" is generally considered to be the period when the moon just appeared, that is, evening and dusk.

night

After sunset, it means at night.