Pietism, n.
Etymology: [Cf. G. pietismus, F. piétisme.]
1. The principle or practice of the Pietists.
2. Strict devotion; also, affectation of devotion. The Schöne Seele, that ideal of gentle pietism, in "Wilhelm Meister." W. Pater.
Shades of meaning
Fernald has no entry of its own for pietism; he lists it under hypocrisy, religion.
Where he writes about it:
Pietism, originally a word of good import, is now chiefly used for an unregulated emotionalism; formalism is an exaggerated devotion to forms, rites, and ceremonies, without corresponding earnestness of heart; sham (identical in origin with shame) is a trick or device that puts one to shame, or that shamefully disappoints expectation or falsifies appearance. — from hypocrisy
Piety is primarily filial duty, as of children to parents, and hence, in its highest sense, a loving obedience and service to God as the Heavenly Father; pietism often denotes a mystical, sometimes an affected piety; religion is the reverent acknowledgment both in heart and in act of a divine being. — from religion