noun
dark night in the rainy season
A poetic seasonal word (kigo) for late spring/early summer, referring to the deep darkness of a night during the rainy season (tsuyu), especially when the moon is hidden by clouds. Used in haiku and literary contexts.
五月闇の夜、雨音だけが聞こえていた。
On a dark rainy-season night, only the sound of rain could be heard.
五月雨 refers to the early summer rain itself, while 五月闇 specifically describes the darkness of a night during that rainy period.
Compound of 五月 (satsuki, the fifth month of the lunar calendar, corresponding to early summer) and 闇 (yami, darkness). The word evokes the deep, moonless nights of the rainy season.