2 a promise that something will definitely happen
give (someone) a guarantee: I can’t give you any guarantees at the moment.
guarantee (that): The company has given a guarantee that there will be no job losses.
guarantee against: The tribes wanted secure guarantees against future invasions.
guarantee of: The university insisted on a written guarantee of good conduct from his uncle.
cast-iron guarantee (=one that is completely reliable): We need a cast-iron guarantee that the trade in endangered animals will stop.
Synonyms and related words