guarantee / guaranty are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
guarantee: (noun) a written assurance that some product or service will be provided or will meet certain specifications. (noun) an unconditional commitment that something will happen or that something is true. (noun) a collateral agreement to answer for the debt of another in case that person defaults. (verb) give surety or assume responsibility. (verb) make certain of. (verb) stand behind and guarantee the quality, accuracy, or condition of.
guaranty: NA
guarantee: g·EH·r·ah·n·t·IY
guaranty: g·EH·r·ah·n·t·IY
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)