dark cloud

30 Moby Thesaurus words for "dark cloud":
      Black Magellanic Cloud, Crab Nebula, angry clouds, black cat,
      black clouds, bright diffuse nebula, broken mirror, coalsack,
      dark nebula, diffuse nebula, dust cloud, gaseous nebula,
      gathering clouds, halcyon bird, nebula, nebula of Lyra,
      nebular hypothesis, nebulosity, nebulous stars, owl,
      planetary nebula, rainbow, raven, ring nebula, shooting star,
      storm clouds, stormy petrel, the Coalsack, thundercloud,
      thunderhead