The Collaborative International Dictionary of English v.0.48:

Inoffensive \In"of*fen"sive\, a. [Pref. in- not + offensiue: cf.
   F. inoffensif.]
   1. Giving no offense, or provocation; causing no uneasiness,
      annoyance, or disturbance; as, an inoffensive man, answer,
      appearance.
      [1913 Webster]

   2. Harmless; doing no injury or mischief. --Dryden.
      [1913 Webster]

   3. Not obstructing; presenting no interruption or hindrance.
      [R.] --Milton.
      [1913 Webster]

            So have I seen a river gently glide
            In a smooth course, and inoffensive tide. --Addison.
      -- In"of*fen"sive*ly, adv. -- In"of*fen"sive*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

inoffensive
    adj 1: not causing anger or annoyance; "inoffensive behavior"
           [syn: inoffensive, unoffending] [ant: offensive]
    2: giving no offense; "a quiet inoffensive man"; "a refreshing
       inoffensive stimulant" [ant: offensive]
    3: substituting a mild term for a harsher or distasteful one;
       "`peepee' is a common euphemistic term" [syn: euphemistic,
       inoffensive] [ant: dysphemistic, offensive]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "inoffensive":
   admissible, allowable, benign, condonable, defensible, dispensable,
   excusable, exemptible, expiable, forgivable, harmless, innocent,
   innocuous, justifiable, legitimate, nonmalignant, nonpoisonous,
   nontoxic, nonvirulent, pardonable, reasonable, remissible,
   undamaging, unhurtful, uninjurious, unobjectionable, unobnoxious,
   unoffending, venial, vindicable, warrantable