Noun
Literally means smooth brain.
1. A rare brain formation disorder caused by defective neuronal migration during the 12th to 24th weeks of gestation resulting in a lack of development of brain folds (gyri) and grooves (sulci). It is a form of cephalic disorder. Terms such as ‘agyria’ (no gyri) or ‘pachygyria’ (broad gyri) are used to describe the appearance of the surface of the brain. (wikipedia.org)
2. A disorder characterized by smoothness (lack of folds and grooves) of the brain. (wiktionary.org)
3. Condition in which the brain is smooth owing to failure of development of cerebral gyri. (nanomedicine.com)
Word origin: From Greek lissos, “smooth”