Source : Webster's Revised Unabridged Dictionary (1913)

Gainful \Gain"ful\, a.
   Profitable; advantageous; lucrative. ``A gainful
   speculation.'' --Macaulay. -- {Gain"ful*ly}, adv. --
   {Gain"ful*ness}, n.

Source : WordNet®

gainfully
     adv : in a gainful way; "are you gainfully employed now?"