cumulonimbus
noun [ U ] environment specialized uk/ˌkjuː.mjə.ləʊˈnɪm.bəs/ us/ˌkjuː.mjə.loʊˈnɪm.bəs/
积雨云（一种高空浓密的大积云，能产生大雨或雷暴）
a large, tall type of cumulus cloud that is often dark and brings heavy rain or a thunderstorm
Compare: thundercloud