There are several synonyms for the term "payable on demand," including "immediately payable," "instantly payable," "promptly payable," and "forthwith payable." Other options include "on-call payable," "directly payable," "at once payable," and "without delay payable." These terms are often used when referring to financial transactions, particularly those that involve loans, credit, or other forms of payment. Whether you are a lender or a borrower, it's important to understand the different nuances and implications associated with each synonym, in order to ensure that you are using the right term for your specific needs and circumstances.