lacking

adjective

1. Lacking an essential element: defective, deficient, incomplete, wanting. See better/worse, excess/insufficiency/enough.
2. Deficient in a usual or needed amount: absent, wanting. See excess/insufficiency/enough.
3. Not having a desirable element: barren, destitute, devoid, empty, innocent, void, wanting. Idioms: in want of. See full/empty/capacity.

Definition: wanting, deficient
Antonyms: abundant, enough, full of, having, plentiful, profuse, sufficient

The adjective has 2 meanings:

Meaning #1: not existing
  Synonyms: missing, nonexistent, wanting

Meaning #2: inadequate in amount or degree
  Synonyms: deficient, wanting