- a cloud of a class indicative of thunderstorm conditions, characterized by large, dense towers that often reach altitudes of 30,000 feet (9,000 meters) or more, cumuliform except for their tops, which appear fibrous because of the presence of ice crystals: occurs as a single cloud or as a group with merged bases and separate tops.
- a cumulus cloud of great vertical extent, the top often forming an anvil shape and the bottom being dark coloured, indicating rain or hail: associated with thunderstorms
