1. noun /ˌɡæɹənˈtiː/
a) Anything that assures a certain outcome.
Can you give me a guarantee that he will be fit for the match?
b) A written declaration that a certain product will be fit for a purpose and work correctly.
The cooker comes with a 5-year guarantee.
2. verb /ˌɡæɹənˈtiː/
a) To assure that something will get done right.
The long sunny days guarantee a good crop.
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