rainy season cloud
Archaic term for clouds seen during the rainy season (五月雨, samidare). Not used in modern everyday Japanese; encountered in classical literature or poetry.
Rainy season clouds covered the sky, and the long rain continued.
五月雨 refers to the early summer rainy season itself or the intermittent rain, while 五月雨雲 specifically means the clouds of that season.
Compound of 五月雨 (samidare, 'early summer rainy season') and 雲 (kumo, 'cloud'). The exact historical derivation is uncertain, but the term is associated with classical Japanese poetry.