Infirmative
The Cyclopedic Law Dictionary · Walter A. Shumaker and George Foster Longsdorf; ed. James C. Cahill · 1922
The Cyclopedic Law Dictionary
Weakening. Webster.
Tending to weaken or render infirm; disprobabilizing.
3 Benth. Jud. Ev. 13, 14.
Exculpatory is used by some authors as synonymous.
See Wills, Circ. Ev. 120 et seq.; Best, Pres. § 217 et seq.