The Collaborative International Dictionary of English v.0.48:

Ingenious \In*gen"ious\, a. [L. ingeniosus, fr. ingenium innate
   or natural quality, natural capacity, genius: cf. F.
   ing['e]nieux. See Engine.]
   1. Possessed of genius, or the faculty of invention; skillful
      or promp to invent; having an aptitude to contrive, or to
      form new combinations; as, an ingenious author, mechanic.
      [1913 Webster]

            A man . . . very wise and ingenious in feats of war.
                                                  --Hakluyt.
      [1913 Webster]

            Thou, king, send out
            For torturers ingenious.              --Shak.
      [1913 Webster]

            The more ingenious men are, the more apt are they to
            trouble themselves.                   --Sir W.
                                                  Temple.
      [1913 Webster]

   2. Proceeding from, pertaining to, or characterized by,
      genius or ingenuity; of curious design, structure, or
      mechanism; as, an ingenious model, or machine; an
      ingenious scheme, contrivance, etc.
      [1913 Webster]

            Thus men go wrong with an ingenious skill. --Cowper.
      [1913 Webster]

   3. Witty; shrewd; adroit; keen; sagacious; as, an ingenious
      reply.
      [1913 Webster]

   4. Mental; intellectual. [Obs.]
      [1913 Webster]

            A course of learning and ingenious studies. --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ingenious
    adj 1: showing inventiveness and skill; "a clever gadget"; "the
           cunning maneuvers leading to his success"; "an ingenious
           solution to the problem" [syn: clever, cunning,
           ingenious]