The Collaborative International Dictionary of English v.0.48:

Inadvertent \In`ad*vert"ent\, a. [Cf. F. inadvertant. See 2d
   In-, and Advert.]
   Not turning the mind to a matter; heedless; careless;
   negligent; inattentive.
   [1913 Webster]

         An inadvertent step may crush the snail
         That crawls at evening in the public path. --Cowper.
   -- In`ad*vert"ent*ly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

inadvertently
    adv 1: without knowledge or intention; "he unwittingly deleted
           the references" [syn: unwittingly, inadvertently,
           unknowingly] [ant: advertently, heedfully,
           knowingly, mindfully, wittingly]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "inadvertently":
   carelessly, heedlessly, inconsiderately, indeliberately,
   involuntarily, lightly, negligently, permissively, remissly,
   scampingly, skimpingly, slightingly, slurringly, thoughtlessly,
   unadvisedly, uncalculatedly, undesignedly, unintentionally,
   unpremeditatedly, unreasoningly, unrigorously, unthinkingly,
   unthoughtfully, without premeditation, without willing