Cumuliform refers to the cloud formation that resembles a heap or a pile. Its antonyms would, therefore, be related to cloud formations that are different in shape, such as stratus and cirrus clouds. Stratus clouds are horizontally stretched and tend to cover the whole sky resulting in an overcast appearance. Cirrus clouds, on the other hand, are thin and wispy, appearing high up in the sky. They often indicate fair weather. Other antonyms to cumuliform include altostratus clouds, which are gray and layered, and nimbostratus clouds that are thick and often associated with precipitation events. Knowing these antonyms will help in identifying specific cloud formations and predict upcoming weather conditions.