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):

profitable
    adj 1: yielding material gain or profit; "profitable speculation
           on the stock market" [ant: unprofitable]

Moby Thesaurus II by Grady Ward, 1.0:

107 Moby Thesaurus words for "profitable":
   advantageous, advisable, aidful, appropriate, auspicious, banausic,
   becoming, befitting, beneficial, benevolent, bon, bonny, braw,
   breadwinning, bueno, capital, cogent, commendable, compensating,
   compensative, compensatory, conducive, congruous, constructive,
   contributory, convenient, decent, desirable, effective, elegant,
   estimable, excellent, expedient, fair, famous, fat, favorable,
   feasible, felicitous, fine, fit, fitten, fitting, fructuous,
   fruitful, furthersome, gainful, good, good for, goodly, grand,
   happy, healthy, helpful, kind, laudable, likely, lucrative, meet,
   moneymaking, nice, noble, of value, opportune, paying, pleasant,
   politic, positive, productive, proper, recommendable, regal,
   remedial, remunerative, reparative, repaying, retributive,
   retributory, rewardful, rewarding, right, royal, salutary,
   satisfying, seasonable, seemly, serviceable, skillful, sortable,
   sound, splendid, suitable, therapeutic, timely, to be desired,
   useful, utilitarian, valid, valuable, very good, virtuous,
   well-paying, well-spent, well-timed, wise, worthwhile,
   yielding a return