WordNet (r) 3.0 (2006):

cultism
    n 1: devotion to the doctrine or a cult or to the practices of a
         cult
    2: religious zeal; the willingness to serve God [syn:
       idolatry, devotion, veneration, cultism]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "cultism":
   Sabbatarianism, adoration, celebration, ceremonialism, churchgoing,
   co-worship, conformity, cult, cultus, devotedness, devotion,
   devoutness, dulia, dutifulness, faith, faithfulness, formalism,
   homage, hyperdulia, idolatry, ism, latria, liturgics, liturgiology,
   liturgism, love of God, mystique, observance, pietism, piety,
   piousness, prostration, religion, religionism, religiousness,
   reverence, ritualism, rituality, ritualization, sabbatism,
   sacramentalism, sacramentarianism, solemn observance,
   solemnization, symbolics, symbolism, theism, transcendent wonder,
   veneration, worship, worshipfulness, worshiping