The Collaborative International Dictionary of English v.0.48:

Offenseless \Of*fense"less\, a.
   Unoffending; inoffensive.

   Syn: offenceless.
        [1913 Webster]

WordNet (r) 3.0 (2006):

offenseless
    adj 1: incapable of offending or attacking [syn: offenseless,
           offenceless]