Paying, gainful, remunerative, lucrative, profitable share the meaning of bringing in a return in money.
Paying often implies only such a return, but it may imply a satisfactory return for the labor or effort or expenditure involved (as in a venture, a business, or a trade).
Gainful applies chiefly to an endeavor (as a business or a trade) that leads to a money return whether large or small, but it may apply to persons or their acts that are motivated by a desire for gain.
Remunerative suggests a rewarding of labor, effort, or expenditure and often implies a profit or recompense that exceeds what is usual or customary.
Lucrative carries a stronger implication of large returns and applies to a business, trade, or profession or to an enterprise or undertaking that succeeds beyond one's hopes.
Profitable also is applied to what is rewarding, but it need not imply a money return (see BENEFICIAL ); however it usually suggests such returns, not necessarily in a lucrative manner but in any degree that is consonant with one's wishes or hopes.