Down syndrome

WordReference Random House Unabridged Dictionary of American English © 2026

Down′ syn′drome, [Pathol.]

1. Pathology a genetic disorder, associated with the presence of an extra chromosome 21, characterized by mild to severe mental retardation, weak muscle tone, a low nasal bridge, and epicanthic folds at the eyelids.

Also, Down's syndrome. Formerly, mongolism. Also called trisomy 21. 

• after John Latin. H. Down (1828–96), British physician 1960–65