The Collaborative International Dictionary of English v.0.48:

Inane \In*ane"\, a. [L. inanis.]
   Without contents; empty; void of sense or intelligence;
   purposeless; pointless; characterless; useless. "Vague and
   inane instincts." --I. Taylor. -- In*ane"ly, adv.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Inane \In*ane"\, n.
   That which is void or empty. [R.]
   [1913 Webster]

         The undistinguishable inane of infinite space. --Locke.
   [1913 Webster]

WordNet (r) 3.0 (2006):

inane
    adj 1: devoid of intelligence [syn: asinine, fatuous,
           inane, mindless, vacuous]