The Collaborative International Dictionary of English v.0.48:

Sanctitude \Sanc"ti*tude\, n. [L. sanctitudo.]
   Holiness; sacredness; sanctity. [R.] --Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sanctitude
    n 1: the quality of being holy [syn: holiness, sanctity,
         sanctitude] [ant: unholiness]