'Weakener' definitions:

Definition of 'weakener'

From: WordNet
noun
That which weakens or causes a loss of strength; "doubt is a great weakener of resolve"

Definition of 'Weakener'

From: GCIDE
  • Weakener \Weak"en*er\, n. One who, or that which, weakens. "[Fastings] weakeners of sin." --South. [1913 Webster]