Does Deficient Mean Lacking?

lacking some element or characteristic; defective: deficient in taste. insufficient; inadequate: deficient knowledge.

Does deficiency mean lack?

the state of being deficient; lack; incompleteness; insufficiency. the amount lacked; a deficit.

What does it mean if something is deficient?

1 : lacking in some necessary quality or element deficient in judgment bones deficient in calcium. 2 : not up to a normal standard or complement (see complement entry 1 sense 1b(1)) : defective deficient strength …