Source : Webster's Revised Unabridged Dictionary (1913)

Neglectful \Neg*lect"ful\, a.
   Full of neglect; heedless; careless; negligent; inattentive;
   indifferent. --Pope.

         A cold and neglectful countenance.       --Locke.

         Though the Romans had no great genius for trade, yet
         they were not entirely neglectful of it. --Arbuthnot.
   -- {Neg*lect"ful*ly}, adv. -- {Neg*lect"ful*ness}, n.

Source : WordNet®

neglectfully
     adv : in a neglectful manner