Pronunciation: (ing'kus),[key] —n., —pl.in•cu•desPronunciation: (in-kyOO'dēz)[key]for 1;in•cusfor 2. 1. Anat.the middle one of a chain of three small bones in the middle ear of humans and other mammals. Cf. malleus, stapes. See diag. under ear. 2. Also called anvil, anvil cloud, anvil top, thunderhead. the spreading, anvil-shaped, upper portion of a mature cumulonimbus cloud, smooth or slightly fibrous in appearance.