Infirmative fact
Black's Law Dictionary · Henry Campbell Black, M.A. · 1910
Black's Law Dictionary
In the law of evidence. A fact set up, proved, or even supposed, in opposition to the criminative facts of a case, the tendency of which is to weaken the force of the inference of guilt deducible from them.
3 Benth. Jud. Ev. 14; Best, Pres. § 217, et seq.