one-action rule.In debtor-creditor law, the principle that when a debt is secured by real property, the creditor must foreclose on the collateral before proceeding against the debtor’s unsecured assets. — Also termed one-form-of-action rule. [Cases: Mortgages 218.4, 337, 411.C.J.S. Mortgages §§ 325–326, 335, 456, 473, 494, 581.]

[Blacks Law 8th]