from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A writ whereby a private individual who assists a prosecution can receive all or part of any penalty imposed.
from The Century Dictionary and Cyclopedia
- n. In law, an action on a penal statute, brought partly at the suit of the people or state and partly at that of an informer: so called from the words of the old common-law writ, “Qui tam pro domino rege quam pro se ipso,” etc.
Latin qui tam pro domino rege quam pro se ipso in hac parte sequitur, "[he] who sues in this matter for the king as [well as] for himself". (Wiktionary)