1. A person who gives a guarantee or pledge; one who assumes responsibility for another's debt or obligation if that person fails to pay or perform
The bank required a guarantor before approving the loan for the young entrepreneur.
O banco exigiu um fiador antes de aprovar o empréstimo para o jovem empresário.
2. One who provides security or assurance that something will happen or that a promise will be kept
She agreed to be a guarantor for her brother's rental agreement.
Ela concordou em ser fiadora do contrato de aluguel de seu irmão.