deficient

Lacking something essential; often construed with in.

They were deficient in social skills.

Insufficient or inadequate in amount.

Apothecia lecanoroid; multilocular; each cell containing a single theke; paraphyses deficient.

Of a number n, Having the sum of divisors σ(n)<2n, or, equivalently, the sum of proper divisors (or aliquot sum) s(n)<n.

A person who is deficient.

This was justified by the rationale that mental deficients, by definition, are not able to succeed in society.