Source : Webster's Revised Unabridged Dictionary (1913)

Painless \Pain"less\, a.
   Free from pain; without pain. -- {Pain"less*ly}, adv. --
   {Pain"less*ness}, n.

Source : WordNet®

painless
     adj 1: requiring little hard work or exertion; "a painless solution
            to the problem"
     2: not causing physical or psychological pain; "painless
        dentistry" [ant: {painful}]
     3: with as little pain as possible; "a humanely painless
        killing"