Vadiare Duellum
Defined in 3 dictionaries — Cyclopedic (1922), Ballentine's (1916), Black's (1910)
The Cyclopedic Law Dictionary
Walter A. Shumaker and George Foster Longsdorf; ed. James C. Cahill · 1922
To wage combat. Where two contending parties, on a challenge, give and take a mutual pledge of fighting. Cowell. VADIARE LEGEM (L. Lat) In old English law. To wage law; to give gage or security to make one's law at a day assigned. Spelman.
Ballentine's Law Dictionary
James A. Ballentine · 1916
To engage in combat; to wage battel. See Wager of battel.
Black's Law Dictionary
Henry Campbell Black, M.A. · 1910
L. Lat.
In old English law. To wage or gage the duellum; to wage battel; to give pledges mutually for engaging in the trial by combat.