A person who makes a guarantee or promises to be responsible if someone else fails to do something.
From guarantee (itself from Old French garantir, 'to protect') plus the agent suffix -er. The word evolved in English legal language during the 14th-15th centuries.
A guaranteer isn't guaranteeing themselves—they're staking their reputation on someone else's promise, which is why banks often want your parents to be guaranteers on loans!
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