The Collaborative International Dictionary of English v.0.48:

Studious \Stu"di*ous\, a. [L. studious: cf. F. studieux. See
   Study.]
   1. Given to study; devoted to the acquisition of knowledge
      from books; as, a studious scholar.
      [1913 Webster]

   2. Given to thought, or to the examination of subjects by
      contemplation; contemplative. --Locke.
      [1913 Webster]

   3. Earnest in endeavors; aiming sedulously; attentive;
      observant; diligent; -- usually followed by an infinitive
      or by of; as, be studious to please; studious to find new
      friends and allies.
      [1913 Webster]

            You that are so studious
            Of my affairs, wholly neglect your own. --Massinger.
      [1913 Webster]

   4. Planned with study; deliberate; studied.
      [1913 Webster]

            For the frigid villainy of studious lewdness, . . .
            with apology can be invented?         --Rambler.
      [1913 Webster]

   5. Favorable to study; suitable for thought and
      contemplation; as, the studious shade. [Poetic]
      [1913 Webster]

            But let my due feet never fail
            To walk the studious cloister's pale. --Milton.
      [1913 Webster] -- Stu"di*ous*ly, adv. --
      Stu"di*ous*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

studiousness
    n 1: diligent study