The Modern Standard Chinese pronunciation of Yu (雨 Pinyin Yǔ) “Rain” is yǔ in level forth tone.
雨 in characters and words refer to rain 🌧, related to rain ☔️ like in 雨傘 (yŭsăn) umbrella☂ 🌂 or 雨衣 (yŭyī) raincoat etc. 雨 also can be used as a radical, like a sub-component of another Chinese character.
The Chinese character 雨 🌧 was initially drawn in pictograph 🌧 a cloud with drops of rain falling from it.
Pictographs are the oldest kind of Chinese character. It is usually originated from physical resemblance to the objects they represented, for examples sun, mountain, water, animals in picture form.
Also, see https://en.wiktionary.org/wiki/雨