(of an animal) Having a brain which is naturally smooth in appearance. / (of a human) Lissencephalic; having a brain which lacks convolutions due to malformation.

(slang, derogatory) An incredibly unintelligent person.

plural of bubble brain

(informal, derogatory) Extremely stupid

A showdown between people of high intellect.

(US, slang, derogatory, childish) A very stupid person.

plural of booger brain

plural of Matrioshka brain

(science fiction) A hypothetical megastructure of immense computational capacity powered by a Dyson sphere.

Empty-headed; foolish.