ˈfeɪ.lɪŋ ˈwiːk.nəs the property of lacking physical or mental strength; liability to failure under pressure or stress or strain his weakness increased as he became older the weakness of the span was overlooked until it collapsed powerlessness revealed by an inability to act in spite of their weakness the group remains active a penchant for something even though it might not be good for you he has a weakness for chocolate a flaw or weak point he was quick to point out his wife's failings the condition of being financially weak the weakness of the dollar against the yen