Definition of plum rains in US English:

plum rains

noun

  • (A season of) rainfall in early summer and midsummer in Japan and southern China; also occasionally in singular.

Origin

Late 19th century; earliest use found in Littell's Living Age. After Japanese baiu rainy season, lit. ‘plum rains’ (referring to the time of year when plums ripen): see bai-u, or alternatively synonymous Japanese ume no ame, lit. ‘plums' rains’.