Source : Webster's Revised Unabridged Dictionary (1913)

Reckless \Reck"less\, a. [AS. reccele['a]s, r[=e]cele['a]s.]
   1. Inattentive to duty; careless; neglectful; indifferent.
      --Chaucer.

   2. Rashly negligent; utterly careless or heedless.

            It made the king as reckless as them diligent. --Sir
                                                  P. Sidney.

   Syn: Heedless; careless; mindless; thoughtless; negligent;
        indifferent; regardless; unconcerned; inattentive;
        remiss; rash. -- {Reck"less*ly}, adv. --
        {Reck"less*ness}, n.

Source : WordNet®

recklessly
     adv : in a reckless manner