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):

inadvertent
    adj 1: happening by chance or unexpectedly or unintentionally ;
           "with an inadvertent gesture she swept the vase off the
           table"; "accidental poisoning"; "an accidental shooting"
           [syn: accidental, inadvertent]