The Collaborative International Dictionary of English v.0.48:

dissociate \dis*so"ci*ate\ (d[i^]s*s[=o]"sh[i^]*[=a]t), v. t.
   [imp. & p. p. Dissociated; p. pr. & vb. n. Dissociating.]
   [L. dissociatus, p. p. of dissociare to dissociate; dis- +
   sociare to unite, associate, socius companion. See Social.]
   To separate from fellowship or union; to disunite; to
   disjoin; as, to dissociate the particles of a concrete
   substance.
   [1913 Webster]

         Before Wyclif's death in 1384, John of Gaunt had openly
         dissociated himself from the reformer.   --A. W. Ward.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dissociate
    v 1: part; cease or break association with; "She disassociated
         herself from the organization when she found out the
         identity of the president" [syn: disassociate,
         dissociate, divorce, disunite, disjoint]
    2: regard as unconnected; "you must dissociate these two
       events!"; "decouple our foreign policy from ideology" [syn:
       decouple, dissociate] [ant: associate, colligate,
       connect, link, link up, relate, tie in]
    3: to undergo a reversible or temporary breakdown of a molecule
       into simpler molecules or atoms; "acids dissociate to give
       hydrogen ions"

Moby Thesaurus II by Grady Ward, 1.0:

53 Moby Thesaurus words for "dissociate":
   abrupt, abstract, alienate, cast off, cast out, catalyze,
   cut adrift, cut off, cut out, delete, depart, detach, dialyze,
   disarticulate, disassociate, disconnect, disengage, disjoin,
   disjoint, distance, disunite, divide, divorce, eject, electrolyze,
   estrange, expel, hydrolyze, isolate, leave, part, photolyze,
   pull away, pull back, pull out, segregate, separate, sequester,
   set apart, set aside, sever, shut off, split, stand aloof,
   stand apart, stand aside, step aside, subtract, throw off,
   throw out, uncouple, unyoke, withdraw