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]

WordNet (r) 3.0 (2006):

inanely
    adv 1: vacuously or complacently and unconsciously foolish [syn:
           fatuously, inanely]