The Collaborative International Dictionary of English v.0.48:

Rebuff \Re*buff"\ (r[-e]*b[u^]f"), n. [It. ribuffo, akin to
   ribuffare to repulse; pref. ri- (L. re-) + buffo puff. Cf.
   Buff to strike, Buffet a blow.]
   1. Repercussion, or beating back; a quick and sudden
      resistance.
      [1913 Webster]

            The strong rebuff of some tumultuous cloud.
                                                  --Milton.
      [1913 Webster]

   2. Sudden check; unexpected repulse; defeat; refusal;
      repellence; rejection of solicitation.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rebuff \Re*buff"\, v. t. [imp. & p. p. Rebuffed
   (r[-e]*b[u^]ft"); p. pr. & vb. n. Rebuffing.]
   To beat back; to offer sudden resistance to; to check; to
   repel or repulse violently, harshly, or uncourteously.
   [1913 Webster] re-build

WordNet (r) 3.0 (2006):

rebuff
    n 1: a deliberate discourteous act (usually as an expression of
         anger or disapproval) [syn: rebuff, slight]
    2: an instance of driving away or warding off [syn: rebuff,
       snub, repulse]
    v 1: reject outright and bluntly; "She snubbed his proposal"
         [syn: rebuff, snub, repel]
    2: force or drive back; "repel the attacker"; "fight off the
       onslaught"; "rebuff the attack" [syn: repel, repulse,
       fight off, rebuff, drive back]