The Collaborative International Dictionary of English v.0.48:

Reservation \Res`er*va"tion\ (r?z`?r-v?"sh?n), n. [Cf. F.
   r['e]servation, LL. reservatio. See Reserve.]
   1. The act of reserving, or keeping back; concealment, or
      withholding from disclosure; reserve. --A. Smith.
      [1913 Webster]

            With reservation of an hundred knights. --Shak.
      [1913 Webster]

            Make some reservation of your wrongs. --Shak.
      [1913 Webster]

   2. Something withheld, either not expressed or disclosed, or
      not given up or brought forward. --Dryden.
      [1913 Webster]

   3. A tract of the public land reserved for some special use,
      as for schools, for the use of Indians, etc. [U.S.]
      [1913 Webster]

   4. The state of being reserved, or kept in store. --Shak.
      [1913 Webster]

   5. (Law)
      (a) A clause in an instrument by which some new thing is
          reserved out of the thing granted, and not in esse
          before.
      (b) A proviso. --Kent.
          [1913 Webster]

   Note: This term is often used in the same sense with
         exception, the technical distinction being disregarded.
         [1913 Webster]

   6. (Eccl.)
      (a) The portion of the sacramental elements reserved for
          purposes of devotion and for the communion of the
          absent and sick.
      (b) A term of canon law, which signifies that the pope
          reserves to himself appointment to certain benefices.
          [1913 Webster]

   7. an agreement to have some space, service or other
      acommodation, as at a hotel, a restaurant, or on a public
      transport system, held for one's future use; also, the
      record or receipt for such an agreement, or the
      contractual obligation to retain that accommodation; as, a
      hotel reservation; a reservation on a flight to Dallas; to
      book a reservation at the Ritz.
      [PJC]

   Mental reservation, the withholding, or failing to
      disclose, something that affects a statement, promise,
      etc., and which, if disclosed, would materially change its
      import.
      [1913 Webster]

WordNet (r) 3.0 (2006):

reservation
    n 1: a district that is reserved for particular purpose [syn:
         reservation, reserve]
    2: a statement that limits or restricts some claim; "he
       recommended her without any reservations" [syn:
       reservation, qualification]
    3: an unstated doubt that prevents you from accepting something
       wholeheartedly [syn: mental reservation, reservation,
       arriere pensee]
    4: the act of reserving (a place or passage) or engaging the
       services of (a person or group); "wondered who had made the
       booking" [syn: booking, reservation]
    5: the written record or promise of an arrangement by which
       accommodations are secured in advance
    6: something reserved in advance (as a hotel accommodation or a
       seat on a plane etc.)
    7: the act of keeping back or setting aside for some future
       occasion

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "reservation":
   Indian reservation, allowance, appointment, archives, area,
   arrangement, bank, bespeaking, bird sanctuary, booking, briefing,
   cession, circumscription, concession, condition, demur, demurral,
   demurrer, employment, engagement, exception, exemption,
   extenuating circumstances, forest preserve, game reserve,
   grain of salt, grant, hedge, hedging, hesitancy, hesitation,
   hiring, holding back, library, limitation, mental reservation,
   modification, museum, national forest, national park, objection,
   paradise, park, plot, preengagement, preserve, provision, proviso,
   qualification, qualm, region, reluctance, reserve, restriction,
   retainment, reticence, salvo, sanctuary, scruple, section,
   special case, special treatment, specialness, specification,
   state forest, stipulation, store, string, strings, taking on, term,
   terms, territory, tract, waiver, wilderness preserve,
   wildlife preserve, withholding



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

RESERVATION, contracts. That part of a deed or other instrument which
reserves a thing not in esse at the time of the grant, but newly created. 2
Hill. Ab. 359; 3 Pick. R. 272; It differs from an exception. (q.v.) See 4
Vern. 622; Brayt. R. 230; 9 John. R. 73; 20 John, R. 87; 3 Ridg. P. C. 402;
Co. Litt. 43 a; 2 Tho Co. Litt. 412