noun
passing autumn shower; patchy fall rain
A brief, intermittent shower typical of autumn, often moving in patches. Literary and somewhat poetic; in everyday speech, 秋の通り雨 or にわか雨 are more common.
叢時雨が通り過ぎると、空に虹がかかった。
After the passing autumn shower, a rainbow appeared in the sky.
山里では、むらしぐれが一日に何度も降ったりやんだりする。
In the mountain village, patchy autumn showers come and go many times a day.
Compound of 叢 (むら, 'cluster, patch') and 時雨 (しぐれ, 'autumn/winter drizzle'). The exact historical derivation is uncertain, but the word poetically describes rain that falls in scattered patches.