The Collaborative International Dictionary of English v.0.48:

Isolation \I`so*la"tion\ ([imac]`s[-o]*l[=a]"sh[u^]n), n. [Cf.
   F. isolation.]
   The act of isolating, or the state of being isolated;
   insulation; separation; loneliness. --Milman.
   [1913 Webster]

WordNet (r) 3.0 (2006):

isolation
    n 1: a state of separation between persons or groups
    2: a feeling of being disliked and alone
    3: the act of isolating something; setting something apart from
       others [syn: isolation, closing off]
    4: (psychiatry) a defense mechanism in which memory of an
       unacceptable act or impulse is separated from the emotion
       originally associated with it
    5: a country's withdrawal from international politics; "he
       opposed a policy of American isolation"

Moby Thesaurus II by Grady Ward, 1.0:

148 Moby Thesaurus words for "isolation":
   Jim Crow, X ray, abstraction, alien, alienation, aloneness,
   aloofness, anonymity, apartheid, apartness, autism,
   autistic thinking, avoidance mechanism, blame-shifting, blood bank,
   celibacy, charity ward, clinic, closed meeting, color bar,
   compensation, confidentiality, confidentialness, consultation room,
   cordon, cordon sanitaire, cordoning off, decompensation,
   defense mechanism, delivery room, dereism, dereistic thinking,
   detachment, disarticulation, disassociation, disconnectedness,
   disconnection, discontinuity, disengagement, disjointing,
   disjunction, dislocation, dispensary, displacement, dissociation,
   disunion, division, divorce, divorcement, emergency,
   emotional insulation, escape, escape into fantasy,
   escape mechanism, escapism, ethnocentrism, examining room,
   exclusiveness, executive session, fantasizing, fantasy, fever ward,
   flight, foreigner, hospital room, incognito, incoherence,
   insularity, insulation, intensive care, isolationism,
   keeping apart, know-nothingism, labor room, laboratory, loneliness,
   loneness, lonesomeness, luxation, maternity ward, moving apart,
   narrowness, negativism, nursery, operating room, out-group,
   outcast, outsider, overcompensation, parochialism, parting,
   partition, persona non grata, pharmacy, prison ward, privacy,
   private conference, private room, privatism, privatization,
   projection, psychotaxis, quarantine, quarantine flag, race hatred,
   racial segregation, rationalization, recess, reclusion,
   recovery room, removal, resistance, retirement, retreat,
   rustication, sanitary cordon, seclusion, secrecy, segmentation,
   segregation, semi-private room, separateness, separation,
   separatism, sequestration, single blessedness, snobbishness,
   sociological adjustive reactions, solitariness, solitude,
   splendid isolation, stranger, subdivision, sublimation,
   substitution, subtraction, surgery, therapy, tightness,
   treatment room, ward, wish-fulfillment fantasy, wishful thinking,
   withdrawal, xenophobia, yellow flag, yellow jack, zoning