A person who is habitually unsuccessful or unlucky or who is prejudged to be a failure in life, especially one with a defeatist outlook.
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).