雨 is nearly self-explanatory: a horizontal sky line, a cloud canopy beneath it (the 冂 element), and four raindrops falling. Oracle bone forms show essentially the same scene. Identical across 繁體 / 新字体 / 简体.

More than any other character, 雨 is a productive radical for sky phenomena. Almost everything that falls or shines from above carries the 雨 lid: 雪 (snow), 雲 (cloud), 電 (electricity/lightning), 雷 (thunder), 霜 (frost), 露 (dew), 霧 (fog), 霰 (sleet), 霸 (overlord — originally "moonlight after rain"). Spotting the rain-radical at the top of an unfamiliar character is a near-guarantee of weather/sky meaning.

Mandarin: yǔ, dipping 3rd tone. 下雨 (xià yǔ, "to rain" — literally "rain comes down") is the everyday expression. 雨伞 (yǔsǎn, umbrella), 暴雨 (bàoyǔ, downpour), 雨衣 (yǔyī, raincoat), 大雨 (dàyǔ, heavy rain).

Japanese: on-reading ウ (u) appears in 雨天 (uten, rainy weather) and 風雨 (fūu, wind and rain). The kun-reading あめ (ame) is the everyday word — 雨 (ame, rain), 大雨 (ōame, heavy rain). Note the homophone: 雨 (ame, rain) and 飴 (ame, candy) are different characters but identical in spoken form — context disambiguates. The Japanese pitch accent differs (雨 has high-low, 飴 has low-high), but learners often miss this.

Memory aid: a rectangular cloud holding four falling drops. The character is the picture.