1. (

• guarantee ,
• vouch ,

) give surety or assume responsibility; "I vouch for the quality of my products" ;

2. (

• guarantee ,
• ensure ,
• insure ,
• assure ,
• secure

) make certain of; "This nest egg will ensure a nice retirement for us"; "Preparation will guarantee success!" ;

3. (

• undertake ,
• guarantee ,

) promise to do or accomplish; "guarantee to free the prisoners" ;

4. (

• guarantee ,
• warrant ,

) stand behind and guarantee the quality, accuracy, or condition of; "The dealer warrants all the cars he sells"; "I warrant this information" ;