The Collaborative International Dictionary of English v.0.48:

Reasonable \Rea"son*a*ble\, adv.
   Reasonably; tolerably. [Obs.]
   [1913 Webster]

         I have a reasonable good ear in music.   --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Reasonable \Rea"son*a*ble\ (r[=e]"z'n*[.a]*b'l), a. [OE.
   resonable, F. raisonnable, fr. L. rationabilis. See Reason,
   n.]
   1. Having the faculty of reason; endued with reason;
      rational; as, a reasonable being.
      [1913 Webster]

   2. Governed by reason; being under the influence of reason;
      thinking, speaking or acting rationally, or according to
      the dictates of reason; agreeable to reason; just;
      rational; as, the measure must satisfy all reasonable men.
      [1913 Webster]

            By indubitable certainty, I mean that which doth not
            admit of any reasonable cause of doubting. --Bp.
                                                  Wilkins.
      [1913 Webster]

            Men have no right to what is not reasonable.
                                                  --Burke.
      [1913 Webster]

   3. Not excessive or immoderate; within due limits; proper;
      as, a reasonable demand, amount, price.
      [1913 Webster]

            Let . . . all things be thought upon
            That may, with reasonable swiftness, add
            More feathers to our wings.           --Shak.
      [1913 Webster]

   Syn: Rational; just; honest; equitable; fair; suitable;
        moderate; tolerable. See Rational.
        [1913 Webster]

WordNet (r) 3.0 (2006):

reasonable
    adj 1: showing reason or sound judgment; "a sensible choice"; "a
           sensible person" [syn: reasonable, sensible] [ant:
           unreasonable]
    2: not excessive or extreme; "a fairish income"; "reasonable
       prices" [syn: fair, fairish, reasonable]
    3: marked by sound judgment; "sane nuclear policy" [syn:
       reasonable, sane]

Moby Thesaurus II by Grady Ward, 1.0:

134 Moby Thesaurus words for "reasonable":
   acceptable, admissible, all there, allowable, apparent,
   appropriate, arguable, balanced, believable, bright, budget, cheap,
   clearheaded, clearminded, cogent, commonsense, compos mentis,
   conceivable, conceptive, conceptual, condonable, consequent,
   conservative, controlled, cool, coolheaded, credible, defensible,
   discreet, discursive, dispensable, down-to-earth, earthy, easy,
   economic, economical, economy, equitable, excusable, exemptible,
   expiable, fair, forgivable, frugal, hardheaded, healthy-minded,
   ideational, inexpensive, inoffensive, intellectual, intelligent,
   judicious, just, justifiable, knowing, legitimate, levelheaded,
   logical, low, low-priced, lucid, manageable, matter-of-fact,
   mentally sound, moderate, modest, noetic, nominal, normal,
   not so dumb, of sound mind, pardonable, philosophical, plausible,
   popular, positivistic, practical, practical-minded, pragmatic,
   proper, rational, realist, realistic, reasoned, remissible,
   restrained, right, sane, sane-minded, scientific, scientistic,
   secular, sensible, shabby, shoddy, sober, sober-minded, sophic,
   sound, sound-minded, sound-thinking, straight-thinking,
   strong-minded, suitable, temperate, tenable, thinking, together,
   token, tolerable, understanding, unexcessive, unexpensive,
   unextravagant, unextreme, unideal, unidealistic, unobjectionable,
   unromantic, unsentimental, venial, vindicable, warrantable,
   well-argued, well-balanced, well-founded, well-grounded,
   well-thought-out, wholesome, wise, within means, within reason,
   worldly, worth the money



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

REASONABLE. Conformable or agreeable to reason; just; rational.
     2. An award must be reasonable, for if it be of things nugatory in
themselves, and offering no advantage to either of the parties, it cannot be
enforced. 3 Bouv. Inst. n. 2096. Vide Award.



The Devil's Dictionary (1881-1906):

REASONABLE, adj.  Accessible to the infection of our own opinions.
Hospitable to persuasion, dissuasion and evasion.