The Collaborative International Dictionary of English v.0.48:

Breakup \Break"up`\, Break-up \Break"-up`\, n.
   Disruption; coming apart; a separation and dispersion of the
   parts or members; as, a break-up of a meeting, assembly, or
   dinner party; the break-up of a spacecraft on re-entry into
   the atmosphere.

   Syn: separation, detachment.
        [1913 Webster +PJC]

   2. the termination of a relationship; a break-up of the
      government; the break-up of a marriage; the break-up of a
      business partnership; the break-up of a comedy team.

   Syn: dissolution.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

breakup
    n 1: the termination or disintegration of a relationship
         (between persons or nations) [syn: dissolution,
         breakup]
    2: coming apart [syn: separation, breakup, detachment]

Moby Thesaurus II by Grady Ward, 1.0:

144 Moby Thesaurus words for "breakup":
   ablation, analysis, analyzation, anatomizing, anatomy, apoplexy,
   assay, assaying, atomization, biodegradability, biodegradation,
   bloodbath, bloodless revolution, blue ruin, bouleversement,
   breakdown, breaking down, breaking up, carnage, cataclysm,
   catastrophe, cave, cave-in, clean slate, clean sweep, climax,
   collapse, computer revolution, consumption, convulsion, corrosion,
   corruption, counterrevolution, crack-up, crash, crumbling,
   damnation, deactivation, debacle, decay, decimation, decomposition,
   degradability, degradation, demobilization, depredation,
   desolation, despoilment, despoliation, destruction, detachment,
   devastation, diaspora, diastrophism, diffusion, dilapidation,
   disaster, disbandment, disintegration, disjunction, dismissal,
   disorganization, dispersal, dispersion, disruption, dissection,
   dissolution, division, docimasy, erosion, exfoliation, fit,
   fragmentation, gravimetric analysis, havoc, hecatomb, holocaust,
   incoherence, mildew, mold, overthrow, overturn, oxidation,
   oxidization, palace revolution, paroxysm, parting, perdition,
   proximate analysis, quake, quantitative analysis, radical change,
   ravage, ravages of time, reduction to elements, release,
   resolution, revolt, revolution, revolutionary war, revulsion, ruin,
   ruination, rust, scaling, scattering, segmentation,
   semimicroanalysis, separation, shambles, shattering, shipwreck,
   slaughter, smash, smashup, spasm, split-up, spoilage, spoliation,
   striking alteration, stroke, subdivision, subversion,
   sweeping change, tabula rasa, technological revolution, temblor,
   tidal wave, total change, total loss, transilience, tsunami,
   undoing, upheaval, upset, vandalism, violent change, washout,
   waste, wear, wear and tear, wrack, wrack and ruin, wreck