backwardness

详细解释:n. (无比较级)向后, 相反, 倒, 回顾, 倒向, 落后, 进展缓慢, 迟疑, 智力差, 畏缩
【医】 精神[发育]迟缓

英语解释：

名词 backwardness:

lack of normal development of intellectual capacities同义词：retardation, mental retardation, slowness, subnormality