impair

Short definition from Wiktionary

Verb

1. 1
   To weaken; to affect negatively; to have a diminishing effect on.
2. 2
   To grow worse; to deteriorate.

Adjective

1. 1
   Not fit or appropriate; unsuitable.

Noun

1. 1
   The act of impairing or deteriorating.
2. 2
   The fact of being impaired or having grown worse.
3. 3
   An impairment or deterioration.