noun

• (obsolete) A defect or failing; moral or spiritual degeneracy.
  "In the old days, to my commonplace and unobserving mind, he gave no evidences of genius whatsoever. He never read me any of his manuscripts, […], and therefore my lack of detection of his promise may in some degree be pardoned."

verb

• (transitive, stative) To be without, not to have, to need, to require.
  "My life lacks excitement."
• (intransitive) To be short (of or for something).
  "He'll never lack for company while he's got all that money."
• (intransitive, obsolete) To be in want.
  "The young lions do lack, and suffer hunger […]"
• (obsolete) To see the deficiency in (someone or something); to find fault with, to malign, reproach.
  "That is Mede þe Mayde quod she · hath noyed me ful oft / And ylakked my lemman."