verb

• (transitive) To weaken; to affect negatively; to have a diminishing effect on.
  "In 2016, it was announced that Jones had been diagnosed with primary progressive aphasia, a form of dementia that impairs the ability to communicate."
• (intransitive, archaic) To grow worse; to deteriorate.
  "Flesh may empaire,[…]but reason can repaire."

adj

• (obsolete) Not fit or appropriate; unsuitable.
  "giues he not till iudgement guide his bounty, / Nor dignifies an impaire thought with breath:"

noun

• (obsolete) The act of impairing or deteriorating.
• (obsolete) The fact of being impaired or having grown worse.
• (obsolete) An impairment or deterioration.
  "Suppoſe a mans credit ſhould ſuffer an impair with thoſe whoſe cenſure is not to be valued; yet think, which is worſe, ſhame or ſin? Wilt thou ſin againſt God to ſave thy credit?"