Definition of “weaken” - Learner’s Dictionary

weaken

verb [ I, T ] uk us /ˈwiːkən/
LOSE POWER

to become less strong or powerful, or to make someone or something less strong or powerful:

A number of factors have weakened the economy.
LOSE CONFIDENCE

to become less certain or determined about a decision, or to make someone less determined:

I told him he wasn't having any more money but then I weakened.

(Definition of “weaken” from the Cambridge Learner's Dictionary © Cambridge University Press)