The Collaborative International Dictionary of English v.0.48:

Monomachia \Mon`o*ma"chi*a\, Monomachy \Mo*nom"a*chy\, n. [L.
   monomachia, Gr. ?, fr. ? fighting in single combat; mo`nos
   single, alone + ? to fight.]
   A duel; single combat. "The duello or monomachia." --Sir W.
   Scott.
   [1913 Webster]