The Collaborative International Dictionary of English v.0.48:

Pietism \Pi"e*tism\ (p[imac]"[-e]*t[i^]z'm), n. [Cf. G.
   pietismus, F. pi['e]tisme.]
   1. The principle or practice of the Pietists.
      [1913 Webster]

   2. Strict devotion; also, affectation of devotion.
      [1913 Webster]

            The Sch["o]ne Seele, that ideal of gentle pietism,
            in "Wilhelm Meister."                 --W. Pater.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Pietism
    n 1: 17th and 18th-century German movement in the Lutheran
         Church stressing personal piety and devotion
    2: exaggerated or affected piety and religious zeal [syn:
       religiosity, religionism, religiousism, pietism]