The Collaborative International Dictionary of English v.0.48:

disputant \dis"pu*tant\, a. [L. disputants, p. pr. of disputare:
   cf. F. disputant. See Dispute, v. i.]
   Disputing; engaged in controversy. --Milton.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

disputant \dis"pu*tant\, n.
   One who disputes; one who argues in opposition to another;
   one appointed to dispute; a controvertist; a reasoner in
   opposition.
   [1913 Webster]

         A singularly eager, acute, and pertinacious disputant.
                                                  --Macaulay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

disputant
    n 1: a person who disputes; who is good at or enjoys controversy
         [syn: disputant, controversialist, eristic]