Gainful (10)
I believe the answer is:
profitable
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">gainful</span>' is the definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for profitable that I've seen before include "Cost-effective" , "Rewarding" , "offering good returns" , "useful" , "Money-spinning" .)