阵 (zhèn): The original meaning of this character is a “battle formation” or an “array.” Over time, its meaning expanded to become a measure word for events that happen in short, sudden bursts or waves. You can see this in words like `一阵风 (yí zhèn fēng)`, “a gust of wind.” In `阵雨`, it signifies a “spell” or “burst” of rain.
雨 (yǔ): This is the character for “rain.” It's a classic pictograph, originally drawn to look like drops of water falling from a cloud (represented by the top horizontal line).
When you combine them, 阵雨 (zhènyǔ) literally translates to a “burst of rain” or a “wave of rain,” which perfectly captures the meaning of a brief, sudden shower.