deficient vs thoughtless

deficient

• Lacking something essential; often construed with in. 

• Insufficient or inadequate in amount. 

• 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 deficient. 

thoughtless

• Lacking thought or consideration. 

• Marked by or showing lack of due thought or care; careless. 

• Inconsiderate, inattentive.