Salvus plegius
Defined in 3 dictionaries — Ballentine's (1916), Bouvier (1914), Black's (1910)
Ballentine's Law Dictionary
James A. Ballentine · 1916
A safe-pledge; a surety.
Bouvier's Law Dictionary and Concise Encyclopedia
John Bouvier; revised by Francis Rawle · 1914
A safe pledge; called, also, “ certus plegius a sure pledge. Bract 160 b.
Black's Law Dictionary
Henry Campbell Black, M.A. · 1910
L. Lat. A safe pledge; called, also, "eertum plegius," a sure pledge. Bract foL 160b.