The Collaborative International Dictionary of English v.0.48:

Warfare \War"fare`\, n. [War + OE. fare a journey, a passage,
   course, AS. faru. See Fare, n.]
   [1913 Webster]
   1. Military service; military life; contest carried on by
      enemies; hostilities; war.
      [1913 Webster]

            The Philistines gathered their armies together for
            warfare, to fight with Israel.        --I Sam.
                                                  xxviii. 1.
      [1913 Webster]

            This day from battle rest;
            Faithful hath been your warfare.      --Milton.
      [1913 Webster]

   2. Contest; struggle.
      [1913 Webster]

            The weapons of our warfare are not carnal. --2 Cor.
                                                  x. 4.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Warfare \War"fare`\, v. i.
   To lead a military life; to carry on continual wars.
   --Camden.
   [1913 Webster]

WordNet (r) 3.0 (2006):

warfare
    n 1: the waging of armed conflict against an enemy; "thousands
         of people were killed in the war" [syn: war, warfare]
    2: an active struggle between competing entities; "a price war";
       "a war of wits"; "diplomatic warfare" [syn: war, warfare]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "warfare":
   Kilkenny cats, altercation, argument, bickering, cat-and-dog life,
   combat, competition, conflict, contention, contentiousness,
   contest, contestation, controversy, cut and thrust, debate,
   disputation, dispute, emulation, enmity, fighting, hostility,
   litigation, logomachy, paper war, polemic, quarrel, quarreling,
   quarrelsomeness, rivalry, scrapping, squabbling, strife, striving,
   struggle, tug-of-war, war, war of words, words, wrangling