There are many synonyms that can be used for the term "failure to pay." Some of the most common include default, delinquency, nonpayment, neglect to pay, and refusal to pay. These words all describe the same situation where a person or entity has not paid an amount that was owed. It is important to use these terms accurately, as they can have legal implications. For example, default is often used in contracts to describe a situation where a party has failed to fulfill their obligations. Nonpayment can be used in financial contexts, such as when a loan or bill is not paid. Whatever the context, these synonyms provide a useful way to describe the failure to pay.