thunderhead

The swollen upper portion of a thundercloud, usually associated with the development of a thunderstorm.

One of the round compact swelling cumulus clouds which frequently develop into thunder-clouds.

A rounded mass of cloud, with shining white edges; a cumulus, — often appearing before a thunderstorm.

The top portion of a cumulonimbus cloud, which tend to be flattened or fibery in appearance, and which may be indicative of thunderstorm activity.

a rounded projecting mass of a cumulus cloud with shining edges; often appears before a thunderstorm