guarantee - noun

a written assurance that some product or service will be provided or will meet certain specifications

an unconditional commitment that something will happen or that something is true

a collateral agreement to answer for the debt of another in case that person defaults

guarantee - verb

• give surety or assume responsibility
• make certain of
• promise to do or accomplish
• stand behind and guarantee the quality, accuracy, or condition of

guarantee - thesaurus

assure   ensure   guaranty   insure   secure   undertake   vouch   warrant   warrantee   warranty