guarantee
gua-ran-tee
verb
To formally promise that something will happen or be of a certain quality.
"We guarantee your satisfaction with our service."
noun
A formal promise ensuring quality, performance, or a specific outcome.
"The washing machine has a five-year guarantee."
Thesaurus
Synonyms: vouch, guaranty, assure, ensure, insure, secure, warrant, warrantee, warranty, undertake