The Collaborative International Dictionary of English v.0.48:

Profitable \Prof"it*a*ble\, a. [F. profitable.]
   Yielding or bringing profit or gain; gainful; lucrative;
   useful; helpful; advantageous; beneficial; as, a profitable
   trade; profitable business; a profitable study or profession.
   [1913 Webster]

         What was so profitable to the empire became fatal to
         the
         emperor.                                 --Arbuthnot.
   [1913 Webster] -- Prof"it*a*ble*ness, n. --
   Prof"it*a*bly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

profitableness
    n 1: the quality of being encouraging or promising of a
         successful outcome [syn: favorableness, favourableness,
         advantageousness, positivity, positiveness,
         profitableness] [ant: unfavorableness,
         unfavourableness]
    2: the quality of affording gain or benefit or profit [syn:
       profitableness, profitability, gainfulness,
       lucrativeness] [ant: unprofitability, unprofitableness]