Definition from macmillandictionary.com
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Stress can weaken the immune system.
She began to weaken after running for 8 miles.
Many buildings had already been weakened by last year’s storms.
A peace deal between Israel and Lebanon would have weakened Syria’s influence in the region.
If your facts are wrong, that’s going to weaken your case.
No amount of violence will weaken our resolve.
In the end I weakened and agreed to go.