Winter solstice is the day with the fewest hours of sunlight during the whole year.
This year, in the Northern Hemisphere, it occurs today, on December 21st.
But why is winter called winter?
It was the Proto-Germanic wentruz, with the exact same meaning, that gave rise to the Old English “winter”.
This, in turn, probably derives from the Proto-Indo-European wed, meaning “wet,” or it may come from the Proto-Indo-European wind-, meaning “white”.