QUANTUM DAMNIFICATUS, equity practice. An issue directed by a court of equity to be tried in a court of law, to ascertain by a trial before a jury, the amount of damages suffered by the non-performance of some collateral undertaking which a penalty has been given to secure. When such damages have thus been ascertained the court will grant relief upon their payment. Jer. on Jur. 477; 4 Bouv. Inst. n. 3913.