When it was originally created, the Chinese character for "winter" was drawn as an image that shows a string with knots tied at both of its ends. Like this:
This pictograph, which appeared on Chinese oracle bones, originally meant "end." It attained the meaning of "winter" possibly for two reasons. First, winter was viewed as the "end" of a year. Secondly, in spoken Chinese, the word for "winter" and the word for "end" sound similar.
As time went on, the pictograph for "winter" evolved to be something like this:
As you can see, the top part of the character is an altered form of a string with knots tied on both ends; a lower part was added to stand for ice in winter time. This character was later standardized as 冬.
In China winter solstice is known as Dōng Zhì, 冬至, "Winter Height." That is the day when we see the shortest daylight time and the longest night.
What is known as wax gourd or ash gourd in the West the Chinese call Dōng Guā, 冬瓜, "winter melon." The fruit is so named evidently because its snowy coating (wax, ash), not because it comes to fruition in winter time.
The Chinese character for "winter" pronounces the same as the Chinese word for "east"; the two are homonyms. In both cases, the pronunciation is [dōng]. To avoid confusion, the two words are written differently - 冬 for "winter" and 东 for "east." Now you get a sense why the Chinese keep using characters instead of writing phonetically.