The Collaborative International Dictionary of English v.0.48:

Sinful \Sin"ful\, a. [AAS. synfull.]
   Tainted with, or full of, sin; wicked; iniquitous; criminal;
   unholy; as, sinful men; sinful thoughts. --Piers Plowman.
   [1913 Webster]

         Ah sinful nation, a people laden with iniquity. --Isa.
                                                  i. 4.
   [1913 Webster] -- Sin"ful*ly, adv. -- Sin"ful*ness, n.
   [1913 Webster]