weaken verb
ADV. considerably, greatly, seriously, severely, significantly, substantially | fatally The regime was fatally weakened by the unrest and violence. | further | slightly, somewhat | gradually, progressively Central authority has been progressively weakened since the outbreak of the civil war. | permanently
VERB + WEAKEN begin to | serve to The division of Germany had served to weaken the party. | tend to | be designed to an unusual move designed to weaken the rebels
You can also check other dicts: weaken (English, 中文解释 ), wordnet sense, Collins Definition