qui tam
/ˌkwʌɪ ˈtam/ /ˌkwiː ˈtam/Law
noun
A civil action brought under a criminal statute which allows a private individual to sue for a penalty both personally and on behalf of the Crown (government, or a specified public institution). Also in extended use: †a person who brings such an action, an informer (obsolete ).
adjective
Designating, relating to, or characterized by this type of action.
Origin
Late 17th century. From post-classical Latin qui tam, the first words of the clause qui tam pro domino rege quam pro se ipso sequitur ‘who sues as well for the lord the king as for himself’ from classical Latin quī who + tam so much, to such a degree.