There are several synonyms for the word "weakener" that can be used to describe things or actions that reduce strength or effectiveness. Some examples include "debilitator," "underminer," "detractor," "diminisher," "bluntener," "sap," and "reducer." These words can be used in various contexts, such as the weakening of a metal due to corrosion, the undermining of an argument with weak evidence, or the diminishment of an opponent's power through political means. Whatever the case may be, these synonyms help to add variety and nuance to the English language, allowing writers and speakers to more precisely convey their intended meaning.