霜
しも · shimo · JLPT N3 · noun
frost
❄️ 霜 = rain 雨 + mutual 相: frost is rain's cold partner
The top part 雨 marks weather words (雪 snow, 雲 cloud, 雷 thunder). The bottom 相 gives the Chinese reading sou. For the native reading shimo, link it to shimo 下 meaning below: frost is the weather that settles down low on the ground.
霜 — rain radical 雨 + xiāng 相 (phonetic)
霜 is a semantic-phonetic compound. The top 雨 ('rain') signals a weather phenomenon, while 相 below provides the sound, originally close to 'shuāng'. The character has meant 'frost' since early times, later extending to figurative senses like white hair or yearly cycles ('one frost' = one year).