Entry in progress—B.P.
Merriam-Webster Online Dictionary
Main Entry: gravy train
: a much exploited source of easy money; also : gravy 2a
(Oxford English Dictionary)
Money easily acquired; an unearned or unexpected bonus; a tip. Hence to ride (board) the gravy train (or boat), to obtain easy financial success. slang (orig. U.S.).
1910 Sat. Even. Post 30 July 13/1 Stick him for all you can. You’re a hard worker, and you mustn’t let some~body else git the gravy.
1927 Amer. Speech II. 276 Gravy train, sinecure. 1932 WODEHOUSE Hot Water i. 30 ‘Sixty thousand dollars’ worth, at least.’ Mr. Slattery was impressed. Sixty grand, he agreed, was pretty good gravy.
1933 Amer. Speech Feb. 32/1 Ride a gravy train, to continue to receive more than one’s deserts.
1934 J. O’HARA Appointment in Samarra (1935) 11 If you sell two Cadillacs a month, you make expenses, and anything over that is so much gravy.
1939 E. S. GARDNER D.A. draws Circle (1940) xv. 269 We started riding the gravy train like I said.
1942 D. POWELL Time to be Born (1943) viii. 180 An apartment which he was able to furnish almost completely with ‘gravy’—sofas, mattresses, gadgets pressed on him by earnest manufacturers in hopes of public mention of their products.
1948 MENJOU & MUSSELMAN It Took Nine Tailors 141 Once you get on the Hollywood gravy boat, it is no trick to make money; the trick is to keep it.
1952 M. MCCARTHY Groves of Academe (1953) x. 197 There was a moment in the spring when the whole Jocelyn sideshow seemed to be boarding the gravy train, on to fatter triumphs of platitude and mediocrity.