The Collaborative International Dictionary of English v.0.48:

Separation \Sep`a*ra"tion\, n. [L. separatio: cf. F.
   s['e]paration.]
   The act of separating, or the state of being separated, or
   separate. Specifically:
   (a) Chemical analysis.
   (b) Divorce.
   (c) (Steam Boilers) The operation of removing water from
       steam.
       [1913 Webster]

   Judicial separation (Law), a form of divorce; a separation
      of man and wife which has the effect of making each a
      single person for all legal purposes but without ability
      to contract a new marriage. --Mozley & W.
      [1913 Webster]

WordNet (r) 3.0 (2006):

separation
    n 1: the state of lacking unity [ant: unification, union]
    2: coming apart [syn: separation, breakup, detachment]
    3: the distance between things; "fragile items require
       separation and cushioning" [syn: interval, separation]
    4: sorting one thing from others; "the separation of wheat from
       chaff"; "the separation of mail by postal zones"
    5: the social act of separating or parting company; "the
       separation of church and state"
    6: the space where a division or parting occurs; "he hid in the
       separation between walls"
    7: the termination of employment (by resignation or dismissal)
    8: (law) the cessation of cohabitation of man and wife (either
       by mutual agreement or under a court order) [syn: legal
       separation, separation]
    9: the act of dividing or disconnecting

Moby Thesaurus II by Grady Ward, 1.0:

255 Moby Thesaurus words for "separation":
   Jim Crow, aberration, aesthetic distance, alien, alienation,
   alteration, analysis, analyzation, anatomization, anatomizing,
   anatomy, annulment, apartheid, apartness, assay, assaying,
   atomization, barrier, bolting, brattice, breach,
   breach of friendship, break, breakdown, breaking down, breaking up,
   breakup, broken home, broken marriage, buffer, buffer state,
   bulkhead, bumper, centrifugence, change, clarification, clearance,
   cleavage, cleft, cloison, colature, collision mat, color bar,
   compass, contradistinction, cordon, cordon sanitaire,
   cordoning off, cushion, deactivation, decentralization,
   decree of nullity, deep space, demarcation, demobilization,
   deployment, depths of space, destructive distillation,
   desynonymization, detachment, deviation, diaphragm, diaspora,
   dichotomy, differencing, differentiation, disaffection,
   disassociation, disbandment, disconnection, discrimination,
   disequalization, disfavor, disintegration, disjointedness,
   disjunction, dismemberment, dismissal, disorganization, dispersal,
   dispersion, disruption, dissection, dissepiment, dissociation,
   dissolution, dissolution of marriage, distance, distillation,
   distinction, distinctiveness, distinguishment, disunion, disunity,
   divarication, divergence, divergency, diversification, dividedness,
   dividing line, dividing wall, division, divorce, divorcement,
   docimasy, edulcoration, elution, elutriation, essentialization,
   estrangement, ethnocentrism, exclusiveness, extent, extraction,
   falling-out, fanning, fanning out, farness, fender, filtering,
   filtration, fission, foreigner, fracture, fracturing,
   fragmentation, grasswidowhood, gravimetric analysis, hairsplitting,
   individualization, individuation, infinity, insularity, insulation,
   interlocutory decree, interseptum, isolation, isolationism,
   keeping apart, know-nothingism, leaching, leeway, length,
   light-years, lixiviation, margin, mat, microscopic distinction,
   midriff, midsection, mileage, modification, narrowness,
   nice distinction, nuance, open rupture, out-group, outcast,
   outsider, pad, panel, paries, parochialism, parsecs,
   particularization, parting, partition, party wall, percolation,
   persona non grata, personalization, perspective, piece, privacy,
   privatism, privatization, property line, proximate analysis,
   purification, quantitative analysis, quarantine, quarantine flag,
   race hatred, racial segregation, range, reach,
   recall of ambassadors, recess, reclusion, reduction to elements,
   refinement, release, remoteness, resolution, retirement, retreat,
   riddling, rift, rupture, rustication, sanitary cordon, schism,
   scission, screening, seclusion, secrecy, segmentation, segregation,
   semimicroanalysis, separate maintenance, separateness, separatism,
   septulum, septum, sequestration, severalization, severance,
   shade of difference, shattering, shedding, shock pad, sieving,
   sifting, snobbishness, space, span, specialization,
   spiritualization, splaying, splendid isolation, split, split-up,
   splitting, spread, spreading, spreading out, straining, stranger,
   stretch, stride, subdivision, sublimation, subtle distinction,
   tightness, trichoschistism, trichotomy, variation, wall, way, ways,
   winnowing, withdrawal, xenophobia, yellow flag, yellow jack



Bouvier's Law Dictionary, Revised 6th Ed (1856):

SEPARATION, contracts. When the husband and wife agree to live apart they
are said to have made a separation.
     2. Contracts of this kind are generally made by the husband for himself
and by the wife with trustees. 4 Paige's R. 516; 3 Paige's R. 483; 5 Bligh,
N. S. 339; 1 Dow & Clark, 519. This contract does not affect the marriage,
and the parties may, at any time agree to live together as husband and wife.
The husband who has agreed to a total separation cannot bring an action for
criminal conversation with the wife. Roper, Hush. and Wife, passim; 4 Vin.
Ab. 173; 2 Stark. Ev. 698; Shelf. on Mar. & Div. ch. 6, p. 608.
     3. Reconciliation after separation supersedes special articles of
separation in courts of law and equity. 1 Dowl. P. C. 245; 2 Cox, R. 105; 3
Bro. C. C. 619, n.; 11 Ves. 532. Public policy forbids that parties should
be permitted to make agreements for themselves to hold good whenever they
choose to live separate. 5 Bligh, N. S. 367, 375; and see 1 Carr. & P. 36.
See 5 Bligh, N. S. 339; 2 Dowl. P. C. 332; 2 C. & M. 388; 3 John. Ch. R.
521; 2 Sim. & Stu. 372; 1 Edw. R. 380; Desaus. R. 45, 198; 1 Y. & C. 28; 11
Ves. 526; 2 East, R. 283; 8 N. H. Rep. 350; 1 Hoff. R. 1.