Noun
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.
Source: Webster's dictionaryHesse grew up in a Swabian Pietist household, with the Pietist tendency to insulate believers into small, deeply thoughtful groups. Source: Internet
Bismarck soon adopted his wife's pietism, and he remained a devout Pietist Lutheran for the rest of his life. Source: Internet