The Collaborative International Dictionary of English v.0.48:

Mighty \Might"y\, n.; pl. Mighties.
   A warrior of great force and courage. [R. & Obs.] --1 Chron.
   xi. 12.
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The Collaborative International Dictionary of English v.0.48:

Mighty \Might"y\, adv.
   In a great degree; very. [Colloq.] "He was mighty
   methodical." --Jeffrey.
   [1913 Webster]

         We have a mighty pleasant garden.        --Doddridge.
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The Collaborative International Dictionary of English v.0.48:

Mighty \Might"y\, a. [Compar. Mightier; superl. Mightiest.]
   [AS. meahtig, mihtig; akin to G. m[aum]chtig, Goth. mahteigs.
   See Might, n.]
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   1. Possessing might; having great power or authority.
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            Wise in heart, and mighty in strength. --Job ix. 4.
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   2. Accomplished by might; hence, extraordinary; wonderful.
      "His mighty works." --Matt. xi. 20.
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   3. Denoting an extraordinary degree or quality in respect of
      size, character, importance, consequences, etc. "A mighty
      famine." --Luke xv. 14. "Giants of mighty bone." --Milton.
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            Mighty was their fuss about little matters.
                                                  --Hawthorne.
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WordNet (r) 3.0 (2006):

mighty
    adv 1: (Southern regional intensive) very; to a great degree;
           "the baby is mighty cute"; "he's mighty tired"; "it is
           powerful humid"; "that boy is powerful big now"; "they
           have a right nice place"; "they rejoiced mightily" [syn:
           mighty, mightily, powerful, right]
    adj 1: having or showing great strength or force or intensity;
           "struck a mighty blow"; "the mighty logger Paul Bunyan";
           "the pen is mightier than the sword"- Bulwer-Lytton

Moby Thesaurus II by Grady Ward, 1.0:

207 Moby Thesaurus words for "mighty":
   Atlantean, Brobdingnagian, Cyclopean, Gargantuan, Herculean,
   Homeric, able-bodied, absolute, abysmal, aggrandized, almighty,
   apotheosized, armipotent, ascendant, astronomic, august,
   authoritarian, authoritative, authorized, autocratic, awesome,
   awfully, beatified, beefy, big, bouncing, brawny, bulky, burly,
   canonized, clothed with authority, cogent, colossal, commanding,
   competent, comprehensive, consequential, considerable, controlling,
   deep, deified, dominant, doughty, duly constituted, dynamic,
   effective, elephantine, elevated, eminent, empowered, energetic,
   ennobled, enormous, enshrined, enthroned, epic, ex officio,
   exalted, exceedingly, excellent, exhaustive, extremely, forceful,
   forcible, forcy, full, full-blooded, full-strength, giant,
   giantlike, gigantic, glorified, governing, grand, grave, great,
   gutsy, gutty, hale, hard, hard as nails, hardy, hearty, heavy,
   hefty, hegemonic, hegemonistic, held in awe, heroic, high,
   high and mighty, high-potency, high-powered, high-pressure,
   high-tension, huge, hugely, husky, illustrious, immense, immortal,
   immortalized, imperative, important, imposing, impressive,
   in force, in power, indomitable, infinite, influential, intense,
   iron-hard, irresistible, jumbo, just, large, leading, lofty, lusty,
   magnified, main, mammoth, massive, maximum, mightily,
   mighty in battle, momentous, monocratic, monster, monstrous,
   monumental, mountainous, moving, muscular, nervy, obstinate,
   official, only too, operative, plenary, potent, powerful,
   powerfully, predominant, preeminent, prepotent, prestigious,
   pretty, prodigious, profound, prominent, puissant, quite, ranking,
   rattling, real, really, red-blooded, renowned, right, robust,
   robustious, rugged, ruling, sainted, sanctified, senior, serious,
   shrined, so, stalwart, steely, stout, strapping, striking, strong,
   strong as brandy, strong as strong, strong-willed, stupendous,
   sturdy, sublime, substantial, supereminent, superior, supreme,
   surpassingly, telling, terribly, terrifically, throned, titanic,
   total, totalitarian, towering, tremendous, valid, vast, very,
   vigorous, vital, weighty, well-built, whacking, whopping, wieldy