from
Bouvier's Law Dictionary, Revised 6th Ed (1856)
QUI TAM, remedies. Who as well. When a statute imposes a penalty, for the
doing or not doing an act, and gives that penalty in part to whosoever will
sue for the same, and the other part to the commonwealth, or some
charitable, literary, or other institution, and makes it recoverable by
action, such actions are called qui tam actions, the plaintiff describing
himself as suing as well for the commonwealth, for example, as for himself.
Espin. on Pen. Act. 5, 6; 1 Vin. Ab. 197; 1 Salk. 129 n.; Bac. Ab. h.t.