1 to promise sb that sth will certainly happen or be true, especially if he/she is worried 保证;担保;承诺:
I assure you that it is perfectly safe.我向你保证绝对安全。Let me assure you of my full support.我保证全力支持你。
2 to make sth sure or certain 确定;肯定;确保:
The success of the new product assured the survival of the company.新产品的成功确保了那家公司能生存下去。