The Collaborative International Dictionary of English v.0.48:

Piety \Pi"e*ty\, n. [F. pi['e]t['e]; cf. It. piet[`a]; both fr.
   L. pietas piety, fr. pius pious. See Pious, and cf.
   Pity.]
   1. Veneration or reverence of the Supreme Being, and love of
      his character; loving obedience to the will of God, and
      earnest devotion to his service.
      [1913 Webster]

            Piety is the only proper and adequate relief of
            decaying man.                         --Rambler.
      [1913 Webster]

   2. Duty; dutifulness; filial reverence and devotion;
      affectionate reverence and service shown toward parents,
      relatives, benefactors, country, etc.
      [1913 Webster]

            Conferred upon me for the piety
            Which to my country I was judged to have shown.
                                                  --Milton.
      [1913 Webster]

   Syn: Religion; sanctity; devotion; godliness; holiness. See
        Religion.
        [1913 Webster]

WordNet (r) 3.0 (2006):

piety
    n 1: righteousness by virtue of being pious [syn: piety,
         piousness] [ant: impiety, impiousness]

Moby Thesaurus II by Grady Ward, 1.0:

53 Moby Thesaurus words for "piety":
   Tartuffery, Tartuffism, affectation, affection, allegiance, ardor,
   cant, dedication, deference, devotedness, devotion, devoutness,
   docility, dutifulness, enthusiasm, faithfulness, false piety,
   falseness, fealty, fervor, godliness, goody-goodiness, grace,
   holiness, hypocrisy, insincerity, loyalty, mealymouthedness,
   mummery, obedience, observance, oiliness, passion, pharisaicalness,
   pharisaism, pietism, pietisticalness, piousness, religionism,
   religiosity, religiousness, respect, reverence, sanctimoniousness,
   sanctimony, sanctity, self-righteousness, snivel, snuffle, unction,
   unctuousness, veneration, zeal



Easton's 1897 Bible Dictionary:

Piety
   Lat. pietas, properly honour and respect toward parents (1 Tim.
   5:4). In Acts 17:23 the Greek verb is rendered "ye worship," as
   applicable to God.


The Devil's Dictionary (1881-1906):

PIETY, n.  Reverence for the Supreme Being, based upon His supposed
resemblance to man.

    The pig is taught by sermons and epistles
    To think the God of Swine has snout and bristles.
                                                              Judibras