The word "warranter" refers to someone who gives a guarantee or assurance of something, typically the quality or performance of a product or service. There are several synonyms for this word, including guarantor, sponsor, underwriter, backer, patron, and advocate. A guarantor is someone who pledges to be responsible for fulfilling a contract or repayment obligation if the original borrower defaults. A sponsor is someone who supports a cause, event, or individual financially or through promotion. An underwriter is a financial institution that assumes the risk of another party's financial loss. A backer is someone who provides financial or moral support for a project or venture. A patron is someone who supports an artist or organization. Lastly, an advocate is someone who speaks in favor of a cause or position.