The Collaborative International Dictionary of English v.0.48:

Pious \Pi"ous\, a. [L. pius: cf. F. pieux.]
   1. Of or pertaining to piety; exhibiting piety; reverential;
      dutiful; religious; devout; godly. "Pious hearts."
      --Milton. "Pious poetry." --Johnson.
      [1913 Webster]

            Where was the martial brother's pious care? --Pope.
      [1913 Webster]

   2. Practiced under the pretext of religion; prompted by
      mistaken piety; as, pious errors; pious frauds.
      [1913 Webster]

   Syn: Godly; devout; religious; righteous.
        [1913 Webster]

WordNet (r) 3.0 (2006):

pious
    adj 1: having or showing or expressing reverence for a deity;
           "pious readings" [ant: impious]