The Collaborative International Dictionary of English v.0.48:

Seclusion \Se*clu"sion\, n. [See Seclude.]
   The act of secluding, or the state of being secluded;
   separation from society or connection; a withdrawing;
   privacy; as, to live in seclusion.
   [1913 Webster]

         O blest seclusion from a jarring world, which he, thus
         occupied, enjoys!                        --Cowper.
   [1913 Webster]

   Syn: Solitude; separation; withdrawment; retirement; privacy.
        See Solitude.
        [1913 Webster]

WordNet (r) 3.0 (2006):

seclusion
    n 1: the quality of being secluded from the presence or view of
         others [syn: privacy, privateness, seclusion]
    2: the act of secluding yourself from others

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "seclusion":
   Jim Crow, alien, alienation, aloneness, aloofness, anonymity,
   apartheid, celibacy, closed meeting, color bar, confidentiality,
   confidentialness, cordon, cordon sanitaire, cordoning off,
   detachment, division, ethnocentrism, exclusiveness,
   executive session, foreigner, incognito, insularity, insulation,
   isolation, keeping apart, know-nothingism, loneliness, loneness,
   lonesomeness, moving apart, narrowness, out-group, outcast,
   outsider, parochialism, persona non grata, privacy, private,
   private conference, privateness, quarantine, quarantine flag,
   race hatred, racial segregation, reclusion, retirement,
   sanitary cordon, seclusiveness, segregation, separateness,
   separation, sequestration, single blessedness, snobbishness,
   solitariness, solitude, splendid isolation, stranger, tightness,
   withdrawal, xenophobia, yellow flag, yellow jack