thunderhead

noun Meteorology.

1. incus(def 2).
2. cumulonimbus.
3. the upper portion of a cumulus cloud characterized by dense, sharply defined, cauliflowerlike upper parts and sometimes by great verticality.

noun

1. mainly US and Canadian the anvil-shaped top of a cumulonimbus cloud

n.“high-piled cloud,” 1861, from thunder (n.) + head (n.).