simple past tense and past participle of weaken
"After hours of heavy rain, the bridge was weakened to the point where it could no longer support traffic."
impaired by diminution
"The company's profits were significantly weakened by a sudden drop in sales last quarter."
made weak or weaker
"The long illness had severely weakened his ability to climb the stairs."
Reduced; made less strong.
"The constant rain has weakened the old bridge, making it unsafe for heavy trucks to cross."