The Collaborative International Dictionary of English v.0.48:

Pietist \Pi"e*tist\, n. [Cf. G. pietist, F. pi['e]tiste. See
   Piety.] (Eccl. Hist.)
   One of a class of religious reformers in Germany in the 17th
   century who sought to revive declining piety in the
   Protestant churches; -- often applied as a term of reproach
   to those who make a display of religious feeling. Also used
   adjectively.
   [1913 Webster] Pietistic