Give assurance is a phrase that commonly denotes providing someone with a sense of security or confidence. There are a number of synonyms that can be used to convey this same sentiment, including offer reassurance, provide guarantee, promise surety, commit affirmation, and give pledge. Each of these can be used in a different context depending on the situation, but all have the same underlying meaning of helping to ease someone's doubts or concerns. Whether you're trying to make someone feel more secure in a personal relationship or providing a customer with a guarantee for a product or service, these synonyms can be helpful tools for expressing yourself with clarity and confidence.