PIGNUS

from The Collaborative International Dictionary of English v.0.48

Pignus \Pig"nus\, n.; pl. {Pignora}. [L.] (Rom. Law)
   A pledge or pawn.
   [1913 Webster]

from Bouvier's Law Dictionary, Revised 6th Ed (1856)

PIGNUS, civil law. This word signifies in English, pledge or pawn. (q.v.) It 
is derived, says Gaius, from pugnium, the fist, because what is delivered in 
pledge is delivered. in hand. Dig. 50, 16, 238, 2. This is one of several 
instances of the failure of the Roman jurists, when they attempted 
etymological explanation of words. The elements of pignus (pig) is contained 
in the word p---[?], and its cognate forms. Smith's Dict. Gr. and Rom. 
Antiq. h.v.