A person who is deficient.
Insufficient or inadequate in amount.
Lacking something essential; often construed with in.
Of a number n, Having the sum of divisors σ(n)<2n, or, equivalently, the sum of proper divisors (or aliquot sum) s(n).
A person who is mentally or emotionally damaged.
A person who often makes substantial mistakes; a bungler.
A substantial mistake, usually causing problems for more people than just the person or group who made it.