The Collaborative International Dictionary of English v.0.48:

Harmless \Harm"less\ (h[aum]rm"l[e^]s), a.
   1. Free from harm; unhurt; as, to give bond to save another
      harmless.
      [1913 Webster]

   2. Free from power or disposition to harm; innocent;
      inoffensive. " The harmless deer." --Drayton

   Syn: Innocent; innoxious; innocuous; inoffensive;
        unoffending; unhurt; uninjured; unharmed.
        --Harm"less*ly, adv.- Harm"less*ness, n. Harmonic

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "harmlessness":
   assurance, benignancy, benignity, clear sailing, hurtlessness,
   immunity, innocence, innocuousness, inoffensiveness,
   invulnerability, protection, risklessness, safeguard, safeness,
   safety, security, surety, uninjuriousness, unobnoxiousness