weakener

WordReference Random House Learner's Dictionary of American English © 2025

weak•en /ˈwikən/   v. 

1. to (cause to) become weak or weaker: [no object]
   The animal weakened and eventually died.
   [~ + object]
   A lack of resources will weaken our efforts.

weak•en•er, n. [countable]

WordReference Random House Unabridged Dictionary of American English © 2025

weak•en  (wē′kən), v.t. 

1. to make weak or weaker.
2. Phonetics to change (a speech sound) to an articulation requiring less effort, as from geminate to nongeminate or from stop to fricative.

v.i. 

3. Phonetics, to become weak or weaker.

• weak + -en¹ 1520–30

weak′en•er, n. 
Synonyms

1, 3. enfeeble, debilitate, enervate, undermine, sap, exhaust, deplete, lessen, diminish, lower, reduce, impair, minimize, invalidate.

Antonyms

1, 3. strengthen.