How to use GUARANTEE and how NOT to use it, too

Guarantee as used in legal contexts in English is a "false friend" with similar terms in many other languages. This means that the way you use a term that sounds like guarantee in your language may not be the correct way to use guarantee in English. 

Meaning 1

A agrees to perform B's obligation to C if B doesn't perform it → A is providing a guarantee to C regarding B’s obligation

Meaning 2

A promise that a product or service will have certain characteristics or will achieve certain results → A Corp. will provide a guarantee to B Inc. that its product is defect-free.

Guarantee is also a verb

A is providing a guarantee to C regarding B's obligation (noun) → A is guaranteeing B's obligation to C (verb) 

A Corp. will provide a guarantee to B Inc. that its product is defect-free (noun) → A Corp. will guarantee to B. Inc. that its product is defect-free (verb)

Examples (First meaning)

1. The bank has agreed to give the company a loan, but only because the parent company will guarantee the loan (or will give a guarantee for the loan).
2. My daughter just rented her first apartment, but I had to guarantee her lease.

* When used with this meaning, the term is sometimes written guaranty instead of guarantee 

Examples (Second meaning)

1. The law firm guaranteed that it would finish drafting the contract by Tuesday. 
2. OpenAI does not guarantee that ChatGPT's answers are correct.

Sometimes when you want to say guarantee based on how the equivalent is used in your language, you should instead say → Security or Warranty

Security

The funds or assets that are made available to a creditor to protect it in case a loan is not repaid or an obligation is not complied with are called security, not a guarantee. → The Bank took security over the debtor's assets to secure the loan.

Warranty

Promises in a contract that certain representations are true or a written document or a binding legal document that sets out what will happen if the product or service is defective.