The Collaborative International Dictionary of English v.0.48:

Religiousness \Re*li"gious*ness\, n.
   The quality of being religious.
   [1913 Webster]

WordNet (r) 3.0 (2006):

religiousness
    n 1: piety by virtue of being devout [syn: devoutness,
         religiousness]
    2: the quality of being extremely conscientious; "his care in
       observing the rules of good health amounted to a kind of
       religiousness"