The Collaborative International Dictionary of English v.0.48:

Argumentation \Ar`gu*men*ta"tion\, n. [L. argumentatio, from
   argumentari: cf. F. argumentation.]
   1. The act of forming reasons, making inductions, drawing
      conclusions, and applying them to the case in discussion;
      the operation of inferring propositions, not known or
      admitted as true, from facts or principles known,
      admitted, or proved to be true.
      [1913 Webster]

            Which manner of argumentation, how false and naught
            it is, . . . every man that hath with perceiveth.
                                                  --Tyndale.
      [1913 Webster]

   2. Debate; discussion.
      [1913 Webster]

   Syn: Reasoning; discussion; controversy. See Reasoning.
        [1913 Webster]

WordNet (r) 3.0 (2006):

argumentation
    n 1: a discussion in which reasons are advanced for and against
         some proposition or proposal; "the argument over foreign
         aid goes on and on" [syn: argument, argumentation,
         debate]
    2: a course of reasoning aimed at demonstrating a truth or
       falsehood; the methodical process of logical reasoning; "I
       can't follow your line of reasoning" [syn: argumentation,
       logical argument, argument, line of reasoning, line]