The Collaborative International Dictionary of English v.0.48:

Mild \Mild\ (m[imac]ld), a. [Compar. Milder; superl.
   Mildest.] [AS. milde; akin to OS. mildi, D. & G. mild, OHG.
   milti, Icel. mildr, Sw. & Dan. mild, Goth. milds; cf. Lith.
   melas dear, Gr. ? gladdening gifts.]
   Gentle; pleasant; kind; soft; bland; clement; hence, moderate
   in degree or quality; -- the opposite of harsh, severe,
   irritating, violent, disagreeable, etc.; -- applied to
   persons and things; as, a mild disposition; a mild eye; a
   mild air; a mild medicine; a mild insanity.
   [1913 Webster]

         The rosy morn resigns her light
         And milder glory to the noon.            --Waller.
   [1913 Webster]

         Adore him as a mild and merciful Being.  --Rogers.
   [1913 Webster]

   Mild steel, or Low steel, steel that has but little
      carbon in it and is not readily hardened.
      [1913 Webster]

   Syn: Soft; gentle; bland; calm; tranquil; soothing; pleasant;
        placid; meek; kind; tender; indulgent; clement;
        mollifying; lenitive; assuasive. See Gentle.
        [1913 Webster]

WordNet (r) 3.0 (2006):

mild
    adj 1: moderate in type or degree or effect or force; far from
           extreme; "a mild winter storm"; "a mild fever";
           "fortunately the pain was mild"; "a mild rebuke"; "mild
           criticism" [ant: intense]
    2: humble in spirit or manner; suggesting retiring mildness or
       even cowed submissiveness; "meek and self-effacing" [syn:
       meek, mild, modest]
    3: mild and pleasant; "balmy days and nights"; "the climate was
       mild and conducive to life or growth"; "a soft breeze" [syn:
       balmy, mild, soft]

Moby Thesaurus II by Grady Ward, 1.0:

155 Moby Thesaurus words for "mild":
   Saturnian, accepting, aestival, affable, agreeable, amiable, balmy,
   benign, benignant, bland, blood-hot, blood-warm, bonhomous, bright,
   broken, calid, calm, calming, chastened, choice, clement,
   compassionate, complaisant, conciliatory, cordial, dainty, dead,
   deferential, delicate, demulcent, dilute, diluted, docile,
   domesticated, dovelike, easy, easy-natured, easygoing, emollient,
   equable, equatorial, exquisite, fade, faint, fair, flat,
   flavorless, forbearant, forbearing, forgiving, genial, gentle,
   good-humored, good-natured, good-tempered, gruelly, halcyon,
   housebroken, humane, humble, inane, indifferent, indulgent,
   inoffensive, insipid, jejune, judicious, kind, kindly, lamblike,
   lax, lenient, lenitive, luke, lukewarm, meek, mellow, mellowy,
   merciful, mild as milk, milk-and-water, moderate, modest,
   mollified, mollifying, nonresistive, nonrigid, nonviolent,
   obeisant, obliging, pacific, pacifistic, pappy, passive, patient,
   peaceable, peaceful, placid, pleasant, prudent, pulpy, quiet,
   room-temperature, sapless, savorless, serene, smooth, sober, soft,
   soft as putty, softened, softening, soothing, spiceless, stale,
   subdued, submissive, subservient, subtropical, summery, sunny,
   sunshiny, sweet, sweet-tempered, tame, tamed, tasteless, temperate,
   tender, tepid, thermal, thermic, thin, toasty, tolerant, tractable,
   tranquil, tropical, unassuming, unflavored, unfrozen, unsavory,
   vapid, warm, warm as toast, warmish, washy, watered, watered-down,
   watery, weak, well-natured, whisper-soft, wishy-washy, yielding