The Collaborative International Dictionary of English v.0.48:

Mellow \Mel"low\, v. t. [imp. & p. p. Mellowed; p. pr. & vb.
   n. Mellowing.]
   To make mellow. --Shak.
   [1913 Webster]

         If the Weather prove frosty to mellow it [the ground],
         they do not plow it again till April.    --Mortimer.
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         The fervor of early feeling is tempered and mellowed by
         the ripeness of age.                     --J. C.
                                                  Shairp.
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The Collaborative International Dictionary of English v.0.48:

Mellow \Mel"low\, a. [Compar. Mellower; superl. Mellowest.]
   [OE. melwe; cf. AS. mearu soft, D. murw, Prov. G. mollig
   soft, D. malsch, and E. meal flour.]
   [1913 Webster]
   1. Soft or tender by reason of ripeness; having a tender
      pulp; as, a mellow apple.
      [1913 Webster]

   2. Hence:
      (a) Easily worked or penetrated; not hard or rigid; as, a
          mellow soil. "Mellow glebe." --Drayton
      (b) Not coarse, rough, or harsh; subdued; soft; rich;
          delicate; -- said of sound, color, flavor, style, etc.
          "The mellow horn." --Wordsworth. "The mellow-tasted
          Burgundy." --Thomson.
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                The tender flush whose mellow stain imbues
                Heaven with all freaks of light.  --Percival.
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   3. Well matured; softened by years; genial; jovial.
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            May health return to mellow age.      --Wordsworth.
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            As merry and mellow an old bachelor as ever followed
            a hound.                              --W. Irving.
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   4. Warmed by liquor; slightly intoxicated. --Addison.
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The Collaborative International Dictionary of English v.0.48:

Mellow \Mel"low\, v. i.
   To become mellow; as, ripe fruit soon mellows. "Prosperity
   begins to mellow." --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mellow
    adv 1: (obsolete) in a mellow manner [syn: mellowly, mellow]
    adj 1: unhurried and relaxed; "a mellow conversation" [syn:
           laid-back, mellow]
    2: having a full and pleasing flavor through proper aging; "a
       mellow port"; "mellowed fruit" [syn: mellow, mellowed]
    3: having attained to kindliness or gentleness through age and
       experience; "mellow wisdom"; "the peace of mellow age" [syn:
       mellow, mellowed]
    4: having attained to kindliness or gentleness through age and
       experience; "mellow wisdom"; "the peace of mellow age"
    5: slightly and pleasantly intoxicated from alcohol or a drug
       (especially marijuana) [syn: high, mellow]
    v 1: soften, make mellow; "Age and experience mellowed him over
         the years"
    2: become more relaxed, easygoing, or genial; "With age, he
       mellowed" [syn: mellow, melt, mellow out]
    3: make or grow (more) mellow; "These apples need to mellow a
       bit more"; "The sun mellowed the fruit"

Moby Thesaurus II by Grady Ward, 1.0:

245 Moby Thesaurus words for "mellow":
   achingly sweet, addled, advance, affable, age, aged, agreeable,
   agreeable-sounding, amiable, amicable, appealing, ariose, arioso,
   attain majority, bear fruit, beery, bemused, besotted, blind drunk,
   blissful, bloom, blossom, blow, bring to maturity, canorous,
   cantabile, catchy, cheerful, come of age, come to fruition,
   come to maturity, compatible, complaisant, congenial, cordial,
   crapulent, crapulous, creamy, cushion, delicate, delicious,
   desirable, develop, developed, dizzy, drenched, drunk, drunken,
   dulcet, ease, easy, easygoing, eggshell, en rapport, enjoyable,
   euphonic, euphonious, euphonous, evolute, evolve, fair,
   fair and pleasant, far-gone, felicific, felicitous, fine,
   fine-toned, flat, flavorful, fledge, flourish, flower, fluff,
   flustered, fou, friendly, full, full-blown, full-flavored,
   full-fledged, full-grown, fully developed, gay, genial, gentle,
   giddy, glorious, gloss, golden, golden-tongued, golden-voiced,
   good, good-natured, goodly, gracious, grateful, gratifying, grow,
   grow up, happy, harmonious, heart-warming, honeyed, in full bloom,
   in liquor, inebriate, inebriated, inebrious, intoxicated,
   iridescent, jolly, jovial, juicy, knead, laxate, leave the nest,
   light, likable, limber, limber up, liquid, loosen, luscious, mash,
   massage, maturate, maturated, mature, matured, maudlin, melic,
   mellifluent, mellifluous, mellisonant, mellowed, mellowy, melodic,
   melodious, merry, mild, milden, mollified, mollify,
   mother-of-pearl, muddled, music-flowing, music-like, musical,
   muted, nacreous, nappy, nice, nonresistive, nonrigid, opalescent,
   pale, pastel, patinaed, pearly, plangent, pleasant,
   pleasant-sounding, pleasing, pleasurable, pleasure-giving,
   pleasureful, plump, progress, pulp, pulsing, pure, quiet,
   reach its season, reach manhood, reach maturity, reach twenty-one,
   reach voting age, ready, reeling, relax, resonant, resonating,
   rewarding, rich, ripe, ripen, ripened, rolling, sad, satisfying,
   season, seasoned, semigloss, settle down, shake up, shikker,
   silver-toned, silver-tongued, silver-voiced, silvery, simple,
   singable, smash, sober, sodden, soft, soft as putty, soft-colored,
   soft-hued, soften, soften up, softened, somber, songful, songlike,
   sonorous, sotted, squash, subdue, subdued, subtle, supple, sweet,
   sweet-flowing, sweet-sounding, sweeten, temper, tempered, tender,
   tenderize, throbbing, tiddly, tipsy, toga virilis, tone down,
   tunable, tune down, tuneful, under the influence, vibrant,
   vibrating, warm, wax, welcome, whisper-soft