Source : Webster's Revised Unabridged Dictionary (1913)

Genius \Gen"ius\, n.; pl. E. {Geniuses}; in sense 1, L. {Genii}.
   [L. genius, prop., the superior or divine nature which is
   innate in everything, the spirit, the tutelar deity or genius
   of a person or place, taste, talent, genius, from genere,
   gignere, to beget, bring forth. See {Gender}, and cf.
   {Engine}.]
   1. A good or evil spirit, or demon, supposed by the ancients
      to preside over a man's destiny in life; a tutelary deity;
      a supernatural being; a spirit, good or bad. Cf. {Jinnee}.

            The unseen genius of the wood.        --Milton.

            We talk of genius still, but with thought how
            changed! The genius of Augustus was a tutelary
            demon, to be sworn by and to receive offerings on an
            altar as a deity.                     --Tylor.

   2. The peculiar structure of mind with whoch each individual
      is endowed by nature; that disposition or aptitude of mind
      which is peculiar to each man, and which qualifies him for
      certain kinds of action or special success in any pursuit;
      special taste, inclination, or disposition; as, a genius
      for history, for poetry, or painting.

   3. Peculiar character; animating spirit, as of a nation, a
      religion, a language.

   4. Distinguished mental superiority; uncommon intellectual
      power; especially, superior power of invention or
      origination of any kind, or of forming new combinations;
      as, a man of genius.

            Genius of the highest kind implies an unusual
            intensity of the modifyng power.      --Coleridge.

   5. A man endowed with uncommon vigor of mind; a man of
      superior intellectual faculties; as, Shakespeare was a
      rare genius.

   Syn: {Genius}, {Talent}.

   Usage: Genius implies high and peculiar gifts of nature,
          impelling the mind to certain favorite kinds of mental
          effort, and producing new combinations of ideas,
          imagery, etc. Talent supposes general strength of
          intellect, with a peculiar aptitude for being molded
          and directed to specific employments and valuable ends
          and purposes. Genius is connected more or less with
          the exercise of imagination, and reaches its ends by a
          kind of intuitive power. Talent depends more on high
          mental training, and a perfect command of all the
          faculties, memory, judgment, sagacity, etc. Hence we
          speak of a genius for poetry, painting. etc., and a
          talent for business or diplomacy. Among English
          orators, Lord Chatham was distinguished for his
          genius; William Pitt for his pre["e]minent talents,
          and especially his unrivaled talent for debate.

Source : WordNet®

genius
     n 1: someone who has exceptional intellectual ability and
          originality; "Mozart was a child genius"; "he's smart
          but he's no Einstein" [syn: {mastermind}, {brain}, {Einstein}]
     2: unusual mental ability [syn: {brilliance}]
     3: someone who is dazzlingly skilled in any field [syn: {ace},
        {adept}, {champion}, {sensation}, {maven}, {mavin}, {virtuoso},
         {hotshot}, {star}, {superstar}, {whiz}, {whizz}, {wizard},
         {wiz}]
     4: exceptional creative ability [syn: {wizardry}]
     5: a natural talent; "he has a flair for mathematics"; "he has
        a genius for interior decorating" [syn: {flair}]
     [also: {genii} (pl)]

genii
     See {genius}