weak‧en [intransitive and transitive]
to make someone or something less powerful or less important, or to become less powerful [≠ strengthen]:
Over the last two years the president's position has weakened.
Changes in policy have weakened the power of the trade unions.
The absence of this witness has weakened the case against the accused.
to make someone lose their physical strength, or to become physically weak:
Julia was weakened by her long illness.
to make someone less determined, or to become less determined:
Such policies weaken the resolve of potential troublemakers.
When she begged him to let her stay, he weakened.
to make a building, structure etc less strong, or to become less strong:
The earthquake in Cairo weakened a number of structures.
if a particular country's money or a company's share prices weaken, or if they are weakened, their value is reduced
The pound has weakened against the dollar.