What does "thundercloud" mean?

A large, dark cloud, usually a cumulonimbus, charged with electricity and producing thunder and lightning.

Thundercloud

Common synonyms include: cumulonimbus cloud, alto-cumulus, alto-stratus, angry clouds, anvil cloud, banner cloud.

noun

noun ·Moderate ·College level

Noun

1
A large, dark cloud, usually a cumulonimbus, charged with electricity and producing thunder and lightning.
2
a dark cloud of great vertical extent charged with electricity; associated with thunderstorms wordnet
3
Something menacing and brooding. broadly, figuratively
"the ominous thunderclouds of war"

"A foreboding thundercloud formed in the sky."

From thunder + cloud.