The Collaborative International Dictionary of English v.0.48:

Detachment \De*tach"ment\, n. [Cf. F. d['e]tachement.]
   1. The act of detaching or separating, or the state of being
      detached.
      [1913 Webster]

   2. That which is detached; especially, a body of troops or
      part of a fleet sent from the main body on special
      service.
      [1913 Webster]

            Troops . . . widely scattered in little detachments.
                                                  --Bancroft.
      [1913 Webster]

   3. Abstraction from worldly objects; renunciation.
      [1913 Webster]

            A trial which would have demanded of him a most
            heroic faith and the detachment of a saint. --J. H.
                                                  Newman.
      [1913 Webster]

WordNet (r) 3.0 (2006):

detachment
    n 1: avoiding emotional involvement [syn: withdrawal,
         detachment]
    2: the act of releasing from an attachment or connection [syn:
       detachment, disengagement]
    3: the state of being isolated or detached; "the insulation of
       England was preserved by the English Channel" [syn:
       insulation, insularity, insularism, detachment]
    4: a small unit of troops of special composition
    5: coming apart [syn: separation, breakup, detachment]

Moby Thesaurus II by Grady Ward, 1.0:

348 Moby Thesaurus words for "detachment":
   Jim Crow, KP, Olympian detachment, abstraction, abulia, accidia,
   acedia, adjunct, age group, alienation, aloneness, aloofness,
   anxiety, anxiety equivalent, anxiety state, apartheid, apartness,
   apathy, army, army group, ataraxia, ataraxy, backwardness, band,
   bashfulness, battalion, battery, battle group, benumbedness, bevy,
   blah, blahs, blankness, body, boredom, breakup, brigade, bunch,
   cabal, cadre, carelessness, cast, casualness, catatonic stupor,
   celibacy, chill, chilliness, clearance, clique, cohort, coldness,
   column, comatoseness, combat command, combat team, company,
   complement, component, compulsion, constraint, contingent,
   coolness, corps, coterie, covey, crew, cross section, crowd,
   deactivation, dejection, demobilization, deportation, depression,
   detaching, detail, diaspora, disarticulation, disassociation,
   disbandment, discard, disconnectedness, disconnection,
   discontinuity, discreetness, discretion, disengagement,
   disintegration, disinterest, disinterestedness, disjointing,
   disjunction, dislocation, dismissal, disorganization, dispassion,
   dispassionateness, dispersal, dispersion, disposal, disposition,
   disregard, disregardfulness, dissolution, distance, disunion,
   division, divorce, divorcement, dole, dullness, easygoingness,
   ejection, elation, elimination, emotionalism, equitability,
   eradication, euphoria, evenhandedness, exile, expatriation,
   expressionlessness, expulsion, faction, fairness, field army,
   field train, file, fleet, flying column, folie du doute, fraction,
   frigidity, frostiness, gang, garrison, group, grouping, groupment,
   guardedness, heartlessness, hebetude, heedlessness, hopelessness,
   hypochondria, hysteria, hysterics, iciness, impartiality,
   impassiveness, impassivity, impersonality, in-group,
   inaccessibility, inappetence, inattention, incoherence,
   incuriosity, incuriousness, indifference, indifferentism,
   indifferentness, indiscrimination, inexcitability, insensibility,
   insouciance, installment, intellectual inertia, introversion,
   isolation, isolationism, item, junta, justness, keeping apart,
   kitchen police, lack of affect, lack of appetite, lack of interest,
   lackadaisicalness, languidness, legion, lethargicalness, lethargy,
   liquidation, listlessness, loftiness, loneliness, loneness,
   lonesomeness, luxation, mania, maniple, melancholia,
   mental distress, mindlessness, mob, modesty, movement,
   moving apart, negligence, neutrality, nonchalance, numbness,
   objectivity, obsession, offishness, organization, ostracism,
   out-group, outfit, outlawing, outlawry, pack, parcel, part,
   particular, parting, partition, party, passiveness, passivity,
   pathological indecisiveness, peer group, percentage, phalanx,
   phlegm, phlegmaticalness, phlegmaticness, platoon, plucklessness,
   pococurantism, portion, posse, preoccupation, privacy, privatism,
   privatization, psychalgia, psychomotor disturbance, purge,
   quadrant, quarantine, quarter, quota, random sample, rank, recess,
   recklessness, reclusion, regardlessness, regiment, release,
   remainder, remoteness, removal, repression, reserve, reservedness,
   resignation, resignedness, restraint, reticence, reticency,
   retirement, retreat, riddance, rupture, rustication, salon, sample,
   sampling, seclusion, secrecy, section, sector, segment,
   segmentation, selflessness, separateness, separating, separation,
   separatism, sequestration, set, severance, share,
   single blessedness, sloth, sluggishness, solitariness, solitude,
   sopor, soporifousness, spiritlessness, splendid isolation,
   split-up, spunklessness, squad, squadron, stable, standoffishness,
   stolidity, string, stupefaction, stupor, subdivision, subduedness,
   subgroup, subspecies, subtraction, supineness, suppression,
   suspension, tactical unit, task force, team, tic, torpidity,
   torpidness, torpor, train, tribe, troop, troupe, twitching,
   unaffability, unanxiousness, unapproachability, unbias,
   unbiasedness, unconcern, uncongeniality, undemonstrativeness,
   unexpansiveness, uninquisitiveness, uninterestedness, unit,
   unmindfulness, unopinionatedness, unprejudicedness,
   unresponsiveness, unselfishness, unsolicitousness, wing,
   withdrawal, withdrawnness, zoning