S: (n) guarantee (an unconditional commitment that something will happen or that something is true) "there is no guarantee that they are not lying"
S: (n) guarantee, guaranty (a collateral agreement to answer for the debt of another in case that person defaults)
Verb
S: (v) guarantee, vouch (give surety or assume responsibility) "I vouch for the quality of my products"
S: (v) guarantee, ensure, insure, assure, secure (make certain of) "This nest egg will ensure a nice retirement for us"; "Preparation will guarantee success!"
S: (v) undertake, guarantee (promise to do or accomplish) "guarantee to free the prisoners"
S: (v) guarantee, warrant (stand behind and guarantee the quality, accuracy, or condition of) "The dealer warrants all the cars he sells"; "I warrant this information"