defective
1. de.fec.tive \di-'fek-tiv\ aj 1: wanting in something essential : FAULTY
2: lacking one or more of the usual forms of grammatical inflection {a (R@
verb} 3: markedly subnormal mentally or physically - de.fec.tive.ly av
2. defective n : a person who is subnormal physically or mentally
Webster's English Dictionary