The Collaborative International Dictionary of English v.0.48:

Benign \Be*nign"\, a. [OE. benigne, bening, OF. benigne, F.
   b['e]nin, fem. b['e]nigne, fr. L. benignus, contr. from
   benigenus; bonus good + root of genus kind. See Bounty, and
   Genus.]
   1. Of a kind or gentle disposition; gracious; generous;
      favorable; benignant.
      [1913 Webster]

            Creator bounteous and benign.         --Milton.
      [1913 Webster]

   2. Exhibiting or manifesting kindness, gentleness, favor,
      etc.; mild; kindly; salutary; wholesome.
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            Kind influences and benign aspects.   --South.
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   3. Of a mild type or character; as, a benign disease.
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   Syn: Kind; propitious; bland; genial; salubrious; favorable
        salutary; gracious; liberal.
        [1913 Webster]

WordNet (r) 3.0 (2006):

benign
    adj 1: not dangerous to health; not recurrent or progressive
           (especially of a tumor) [ant: malignant]
    2: pleasant and beneficial in nature or influence; "a benign
       smile"; "the benign sky"; "the benign influence of pure air"
       [syn: benign, benignant] [ant: malign]
    3: kindness of disposition or manner; "the benign ruler of
       millions"; "benign intentions"

Moby Thesaurus II by Grady Ward, 1.0:

109 Moby Thesaurus words for "benign":
   Christian, Christlike, Christly, accommodating, affable,
   affectionate, agreeable, amiable, amicable, auspicious, beneficent,
   beneficial, benevolent, benignant, bland, bracing, bright,
   brotherly, charitable, clement, compassionate, complaisant,
   compliant, congenial, constitutional, cooperative, cordial,
   curable, decent, dexter, fair, favorable, favoring, forbearing,
   fortunate, fraternal, friendly, full of promise, generous, genial,
   gentle, golden, good, good for, good-hearted, gracious, happy,
   harmless, health-enhancing, health-preserving, healthful, healthy,
   human, humane, hygeian, hygienic, indulgent, innocent, innocuous,
   inoffensive, invigorating, kind, kindhearted, kindly,
   kindly-disposed, loving, lucky, merciful, mild, neighborly, nice,
   nonmalignant, nonpoisonous, nontoxic, nonvirulent, obliging,
   of good omen, of happy portent, of promise, overindulgent,
   overpermissive, permissive, promising, propitious, prosperous,
   refreshing, salubrious, salutary, sanitary, softhearted,
   sympathetic, sympathizing, tender, tenderhearted, tonic,
   undamaging, unhurtful, uninjurious, unobnoxious, warm,
   warm-hearted, warmhearted, well-affected, well-disposed,
   well-intentioned, well-meaning, well-meant, white, wholesome