lacking some element or characteristic; defective: deficient in taste.
2.
insufficient; inadequate: deficient knowledge.
–noun
3.
a person who is deficient, esp. one who is mentally defective.
Origin: 1575–85; < L dēficient- (s. of dēficiēns, prp. of dēficere to fail, run short, lack, weaken), equiv. to dē-de-+ fic-, comb. form of facere to make, do1+ thematic -i- + -ent--ent