- mongolism, mongolianism, Down's syndrome, Down syndrome, trisomy 21 - a congenital disorder caused by having an extra 21st chromosome; results in a flat face and short stature and mental retardation
--1 is a kind of trisomy; birth defect, congenital anomaly, congenital defect, congenital disorder, congenital abnormality; retardation, mental retardation, backwardness, slowness, subnormality