The Collaborative International Dictionary of English v.0.48:

Sinless \Sin"less\, a.
   Free from sin. --Piers Plowman.
   [1913 Webster] -- Sin"less*ly, adv. -- Sin"less*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sinlessness
    n 1: the state of being unsullied by sin or moral wrong; lacking
         a knowledge of evil [syn: purity, pureness,
         sinlessness, innocence, whiteness]